USGS Professional Paper 1350, vol. 2 of 2

VOLCANISM IN HAWAII 

Chapter 57 

AA FLOW DYNAMICS, MAUNA LOA 1984 

By Pcter W. Lipman and Norman G. Banks 

ABSTRACT 

The March 25-April 14, 1984. northeut-rift enJption of 

Mauna Loa Volcano, Hawaii, provided an exceptional opportunity 

to atudy development of a large bua.ltic aa Row .yatem 

for leveral ~. The major Row reached 27 Ian from ita 

.ouree vent within a few days of.tart of the eruption, and, fed at 

a rate of about 1()6 m3/h, developed an mitially aimple geographic 

zonation in a.a textural type. and flow morphology. 

Decreaaea in eruption rate during the fu,t few day., to about 

0.4 X t ()6 m 3 /h. triggered a channel blockage and breakout to 

generate a .econd ~r Row on March 29. Without further 

meJor changes in vent output from March 30 through April 7. 

the flow evolved from a single narrow tongue with an efficient 

channel, which delivered virtually the entire vent output to 

within 1 km of the toe. to an uprift-migrating atagoaling channel 

.y.tern chanlcterized by blockage., ponding, and complexly 

branching overflows. Lava production again began to decline 

after April 7, and the rate of upflow stagnation accelerated. 

A major cause of the stagnation wu breakdown in the 

hydraulic efficiency of the channel. Floating channel debris 

{lava boall), created by collapse of portions of the channel 

banks, fonned dams at channel constrictions and caused pond. 

ing, overflows, and lateral breakouts that robbed the lower flow 

of much of its lava supply. UpRow stagnation wu basically due 

to increuing viscosity and yield strength of the channel lava, 

caused by progressive degusing, fonnation of paaty surface 

c1ota, incorporation of channel debris, and ultimately by growth 

of microphenocrysta in lava stored uprih from the vent. 

During the eruption, microphenocryst contents of erupted 

lava increased by nearly two orders of magnitude, from Ie.. 

than 0.5 percent to 30 percent, without concurrent change in 

either bulk magma composition or eruption temperature 

(t,140::t.3 "'C). The microphenocrysta have skeletal mor· 

phologies typical of undercooling. 1be increaae in microphenocryst 

content with time waa paralleled by a dec.rea.ae in 

emi..ion of sulfur and other gues and a decline in lava eruption 

rate. Growth of the microphenocrys.. is interpreted ... crystallization 

from magma that was undercooled 20-30 "'C below 

ita liquidus. The undercooling proabahly re.ulted from aepara· 

tion and reJeaae of volatile. u the magma moved from the 

primary high·level magma reaervoir at a depth of3-5 km below 

the summit caldera to the 2,900-m elevation at the eruption site 

12 km down the northeast rift zone. Analogous increase. in 

microphenocryst content and accompanying uprift stagnation 

of lava Rows have occurred during several earlier historic 

eruptions from Mauna Loa rift zones. 

INTRODUCTION 

lhe eruption of March 25-April 14, 1984, from the northeast 

rift zone of Mauna Loa Volcano, Hawaii, provided an 

exceptional opportunity to observe the development of a major 

basaltic aa flow system, fed by a high-volume eruption for several 

weeks. Similarly large aa Rows were last erupted on Mauna Loa 

from llx, southwest rift zone in 1950 (Fmch and Macdonald. 1953~ 

before the availabi~ty of hdicopters, efficient radio communications, 

abundant high-quality chemical data. devices for accurate temperature 

measurements, and other recent technological advances in 

monitoring techniques. In contrast, recent aa Rows from nearby 

Kilauea Volcano (Moore and others. 1980; Ulrich and others. 

1984) lasted only a few days. y:ere fed at rates an order of 

magnitude smaller than the 1984 Mauna Loa activity, and generally 

were inaccessible to observers except in vent areas and at toes of 

Rows (midzOIles are in heavily vegetated areas lacking helicopter 

landing points~ Detailed recent observations cJ Row dynamics at 

olher volcanoes, notably Etna in Sicily and Arenal in Costa Rica 

(Sparks and others. 1976; Wadge. 1978; Borgia and others. 1983; 

Cigolini and others. 1984), also involved small short-lived Rows. 

At Mauna Loa in 1984. we were able to observe the 

t!Volution, over a three-week period, of a complex aa Row system that 

achieved a maximum length ci 27 km. Initial motivation for these 

observations was to morutor advance of the Row toward the city ci 

Hilo (fig. 57. 'A). As the Row tel1Tlinus stagnated and hazard 

concerns diminished, we became increasingly intrigued by the 

opportunities to ~ complex changes in channel efficiency 

rdated to changing parameters ci lava temperature. density. gas 

content, petrography, and eruption rate. 

Eruption rates were as high as 2.9 X 1()6 m1!h during the first 

six hours of the eruption, stabilized at 0.5 X 1()6-1 x 1()6 m 3 /h for 

the next 12 days, and slowly diminished thereafter. Taal eruptive 

volwne was approximaldy 220 X 1()6 m'. Sizeabk pahoehoe flows 

formed only during the first day of the eruption and within a few 

kilometers of the vent; the remainder ci the RO\>\/' system consisted of 

aa. Especially instructjve ...."ere variations in channel discharge with 

increasing distance from the vent during periods c:l steady-statr lava 

production. vanations in behavior at the Row toe as a function cl 

slopr: and magma supply, development and evolution c:l the aa 

channds. and variations in density. yield strength. and viscosity cl 

the lava 35 functions of lime and distance from the vent. lhe main 

1984 aa Row evolved (without major change to magma discharge at 

the \'ent) from a simple narrow tongue with an efficient channel thal 

delivered virtually the entire lava supply to within I km of the toe, to 

an uprift-stagnating channd system with I~·ees, blockages, poodmg, 

and complexly branching overflows. 

ACKNOWLEDGMENTS 

Our channd observations would not have been feasible Without 

the skillful assistance of helicopter pilots Bill Lacy Jr., Ken Ellard, 

1527 

U.S. Geological Survey Profeuional Paper 1350

1528 VOL£ANISM IN HAWAII 

A 

IS5'40' 

, 

os· 

/ 

'..._. 

II 

/ ! 

L-__I Lmn... 

o 

S 10 KILOMETERS 

1111111 ! II Erupll...e unit 

CONTOUR INTERVAL 1000 PYl(TERS 

lrL L- --'- ~

7. AA FLOW DYNAMICS, MALNA LOA 1984 1529 

Tom Haupmann, and Ed Spencer. W. also thank OUT many 

colleagues, from the uses and academia. who assisted with the 

channd measurements and provided additional obser...ations on the 

1984 eruption: especially j. Buchanan-Banks, D. Clagu., j. Fmk, 

j.P. Lockwood, H.j. Moore, R.B. Moor., T. N.al, M. Rhod.., 

and E. Wolfe. lhoughtful reviews c:l earlier- versions of tlus paper 

by H.j. Moor., D.A. Swanson, and G.E. Ulnch .... greatly 

appreciated. 

CHRONOLOGIC NARRATIVE 

The general evolution c:l the 1984 Mauna Loa eruption 15 

desaibed d5

1530 VOLCANISM IN HAWAII 

A 

FIGURE 57.1.-Acbve Raw front and channels. 1964 Mauna l...or. eruptjon. A. R~lyadnnclII(I; toe 01 Row 1.2030 H.$.t. on March 25. about 2 haws.flCl" lfllltaatlon 

01 ~ veniA. Toe .. at about 2.400-m deY_ion. advanl;lflg at t'Stlmated 2 m1s. Phot~ by R.B. MOOfe. B. VICW uprifllOWMd 2.900.m \ttIlJ on Marclt 27. 

Flow 1 channdJlOQ risht;~~feedRows2and 3onldt. C. Flow Ilocat 1.3SO-mdevation.looIol"IKdc,,",..nmton MMC:h27. ChaMd IS wd1oe overllow, from the channd within 1-2 km rl the 

\tilts. 

TRANSITIONAL LAVA 

Because the transition fTOm pahoehoe to aa occurred within the 

confined channel of flow I during much of the eruption, we had 

ample opportunities to observe this change from a helicopter and 

from observation stations along channel levees. Our observations on 

the 1984 lava are in accord with the interpretations of Macdonald 

(1953) and Pele"on ood Tolling (1980) tha. the troo,ition from 

pahoehoe to aa involves the relation between viscosity and rate of 

mtemal disturbance due to flowage (shear strain~ If Row mechanics 

(Row volume, flow dimensions, slope, momentum) impel pahoehoe to 

continue to I1lCJ'\o'e and deform after it has become highly viscous, the 

lava will change to aa if the critteaJ relation has already been 

approached.. Approach to this critical condition can be rttognized. 

wh

S7. AA FLOW DYNAMICS, MAUNA LOA 1984 1531 

8 

c 

FIGURE 57.2--Continued. 

SLABBY AA 

In the 1984 Mauna Loa eruption, aa flows nearest the 

transition from pahoehoe tended to form slabby aa (also called 

slabby pahoehoe), which consists simply of pahoehoe crust completely 

disrupted in slabs by flowage at a rate too great for the crust 

to accommodate the shear strain plastically (fig. 57.4A). Slabby aa 

was well developed in the advancing terminus of flow I at elevations 

of 2,450-2,600 m, about 3-5 km from the vent. 

SCORIACEOUS AA 

Farther downflow, where the lava was slightly denser and more 

viscous, the surface cf the channel no longer maintained a smooth 

pahoehoe surface crust. Instead, it developf!d scattered lumps or 

clots of relatively cool scoriaceous lava, separated by more fluid 

incandescent lava retaining crude pahoehoe character (fig. 57.48). 

When overflows or breakouts of such scoriaceous aa occurred fairly 

slowly, and flow fronts advanced no faster than 1-2 mlmin, this lava 

type retained its dotted texture as it cooled. The frothy dots 

consisted of red-brown oxidized scoria masses J-30 em across, set 

in dark gray smoother less vesicular lava having a thin poorly 

developed glassy surface. When overflow rates were more rapid, as 

in a sudden sheet-flow breakout through a breached levee, the entire 

surface of the resulting flow disaggregated into sconaceous lumps I 

and the surface of the resulting deposit consists of loose oxidized 

scoria lumps totally covering the dense interior of the aa flow. This 

lava type has at times been called spiney aa (Macdonald and 

Abbott, 1970, p. 26) because of the jagged irregular surfaces of the 

scoria lumps. The front of flow I during its advance on March 

25-26 was dominantly scoriaceous aa between elevations of about 

2,450 and 1,850 m, at distances of 5-12 km from the vent. 

CLiNKERY AA 

Even farther downflow, the active lava surface in the channel 

consisted largely of cooled clots of relatively dense lava that ground 

against each other while riding on top of the more fluid lava core in


¢ 

2600 

~ 

'"~ 

~2000 

~ 

w 

;il1500 

A 

1000 

25 26 27 28 29 30 31 

MARCH 1984 

2 345 6 7 

APRIL 1984 

FICURE 57.3.-Change Ql elevation d lava-flow toes during 1984 Mauna Loa 

eruptIOn. 

B 

the channel. Breakouts and overflows of this material formed dark 

gray dinkery aa, which contrasts with the scoriaceous aa in having 

angular rather than sconaccous surfaces, and in being darker in 

color, less oxidized, and less vesicular. During early advan

AA FLOWAGE ZONES 

Early development of the 1984 aa nO'on (esp«ially now I 

during March 26-29) displayed systematic variations in structure 

and morphology from vent 10 loe-in addition to the aa textural 

types just summarrLed-that can be described in terms of four 

zones: Row toe, lower dispersed flowage, transitional channel. and 

upper stabilized channd (hg. 57.S~ Subsequent development of 

blockages, ponds. and overflows of lava complexly overprinted this 

simple initial aa now zonation. bUI each of the relatively ephemeral 

blockage-overflow lobe! tended to show a similar zonation. 

')] AA Fl..OW DYNAMICS, MAUNA LOA 1984 1533 

Zone of 

dispersed flow 

Row toe 

FLQWTOE 

Early in the eruption, most fealures ci the aa now system """ere 

established within a few kilometers of the Row t~ dunng its 

advance. Upper well-ehannelized parts ri the flow ""'ere stable and 

changed littk as virtually all lava fTlO\..oo efficiently down the 

channel 10 the loe: area. The character of the flow toe varied mainly 

as a function of slope of the local land surface and distance of the toe 

from the slabilized channel. 

Near the vent, on steeper slopes, and where the channel was 

well established close to a Row loe, fluid lava was deli\'ered 

efficiently to lhe Row toe. The result was a rapidly moving broad 

flow front, consisting of scoriaceous or slabby aa, only 1-3 m high 

and with a nearly nat upl"" ,ur(ace (figs. 57.2A. 57.6A~ Such 

rapidly moving fronts exposed the liquid core of lhe aa Row as a 

bright orange band along the enlire Row front; the Row advanced by 

outwelling of the fluid core, which then crusted over, brecciated, and 

overrode its front. This process produced a poorly developed basal 

breccia. because the brecciated upper surface moved more slowly 

than the center of the flow advanced. Such flow fronts tended to form 

sconaceous or clinkery aa. Observed velocities at these Row fronts 

vaned from 50 mIh to as much as S kmlh. ThIs type of RO\\7 fronl 

was o~ during early stages c:J breakouts from the main channel 

where rdatively fluid ponded lava was released as sheet Rows. even 

late in the eruption (fig. S7.6A~ Similar features probably were 

dominant during the early rapid advance of flow I on March 

25-26. 

In contrast. on gentler slopes, at sites more distant from the 

\'mt, and where a broader zone of dispersed flow occurred below 

the channelized Row, the flow toe mO\led more slowly. was higher and 

more irregular in profile, and consisted of denser blockier lava (fig. 

57.68). Little or no fluid material was visible at the flow front, and 

the steep high front advanced by spalling of dense blocks and slabs. 

largely from the breccia layer riding on top of the advancing Row. 

Fine granular to dusty material, resulting from abrasion of aa 

blocks, was a significant constituent at the Aow toe:. Velocities at this 

type of Row front vaned from a maximum of SO mIh to stagnatIon. 

Such Row characterized the fronts of flow I and flow IA dunng therr 

slav.· advance below about I ,3S0 m elevation. 

ZONE OF DISPERSED FLOW 

Behind the advancing toe of the 1984 lava was a zone in which I 

movement was dispersed across much c:J the Row \\1dth and a central 

!- 100_2OO METERS 

FICL-RE ~75.-I:hagrllm UJo"..~ CotlCrutlflg 5l:ructural ft:atur~ tl Q. dYnnd 

,~ 

channel was poorly developed or absent. During rapid advance of 

flow 1 early in the eruption, the zone of dispersed Row was relatively 

short; on March 27 this zone extended only about I km up from the 

toe at the 1,350-m level (figs. 57.2B. S7.n As the eruption 

progressed. the flow toe became more sluggish, and the zone of 

dispersed flowage extended as much as 5-10 km up the flow. 

Observations In this zone "''ere sparse:. because the lava was still hot 

and unstable, and surface features ""ere difficult 10 obsene from 

terrain adjacent to the Row. Movement at the upper surface c:i the 

flow lended to occur along di.screte shears, between which ridges of 

blocky aa moved fairly coherently. ear the toe, the most rapidly 

moving central part of the Aow consisted of blocky aa showmg little 

or no Incandescence; farther upstream, the center of the Row was 

more incandescent and graded into a defined central channel contaimng 

visible fluid lava. Fl()\\., velocities increased gradually from


2500 

~ 

~ 

w 

~ 

w 

~ 

~2000 

Z 

o 

1500 

1000 

25 

;= 

57. AA FLOW DYNAMICS. MAUNA LOA 1964 1535 

A 

c 

8 D 

FIGURE 57.S.-Features d 1tabk-

1536 VOLCJ\NIS~I IN HAWAII 

01 di,persed Row ",'ended 5-10 Ion up from ,he toe ci Row lA, hUI 

the zone of stablized channd flow began to encroach downslope on 

the transition zone. By April 3, the transition zone on flow 1A had 

decreased '0 a length 01 3-4 lon, from about 1,750 '0 1.600-m 

devation. 

STABILIZED CHANNEL ZONE 

As ~ lava lens adjacent to the acti\~ channd cooled and 

marginal defom>aI;oo 01 the flow ceased, all movement hecam< 

concentrated in the cmlral channel, producing a stable geometry in 

upper reaches oI.he flow (fig. 57.8C, O~ Above about 2,450 m, 

where flow I had advanced rapidly as a shed only a few meters thick 

during March 2)-26, the channd appears 10 have stabilized 

rapidly, and there is little evidence for ephemeral devdopment of a 

transition zone. In contrast, the segment from about 2,450-1,650 

m e1evalion, ahhough par' of the ,tahle channel .one hy March 28, 

conlams structures (broad central deprcsstOh. inward-facing sags 

and ndges, and open crack:'. paralld to lhe channel) that mdicate 

that this segment pa.s.scd through a tranMlion zone earlier during ,he 

eruption. By March 28-29, just before the hreak"", of Row IA, 

the lower margm of the stable-channd zooe was al about 

1.850-1,900 m, below channel observalion ,tal;OO 4 aI 1,900 m 

and above station 3 aJong lhc= Power-line Road at 1,600 m (fig. 

57. IB~ By April 3, the Row IA channel had stah;li

57. AA FlDW DYNAMICS. MAUNA LDA 1984 1537 

A 

B 

c 

F 

CruSI on ea,l", channel 

{l 

~ "'- 

t \ ,, 

OeformahOfl levee


- 

--===.==------,.'/;,./'-==:::.'----~/ / /;"/:::=~-- 

7 / St.tion e 7 / Stlltiot'l.. 7 / Stillion 1 

1852 vent Up(>er low.~ 

2500 m Pow...... Ac.d 1800 m 

1900m 

- 

- 

FIGURE 57.IO.-Diawammatic ,cprexntation (plan view) rJ acn:--Row "uatioo 

in flow vdoaty, channel cI Row I-IA. Station Iocatior- ftJwn gn figure 57. lB. 

of aa flows ha~ bttn called accretionary lava baJls and interpreted 

as having fonned "by the rolling up cl viscous lava around some 

fragment fi sofidified lava as a center, in much the ~ way as a 

,nowball rolling downhill" {Wentworth and Macdonald. 1953, p. 

64~ During lilt 1984 eruption, we referred 10 such features as lava 

boats. to emphasize their origin by caving and rafting within the 

active lava channel (fig. S7.IIA~ rather than by rolling on the 

clinkery surface in Iowt:r reaches of the flow. 

Lava boats and more irregular small debris wert observed to 

(onn by caving c:l unstable overhanging channel banks and walls, 

especially when th< 1",,1 of lava in th< channel dropped and so 

reduced ,upport for til. bank (6g. 57.11 B} Caving and rafting of 

the channel banks was aided by the presence of still-plastic lava 

und... til. channel margins (fig. 57. 9~ particularly adjacent 10 

marginal shtan mthe transition zon~. In the zone c:i stabi.li.z.cd flow, 

som~ ~rhangs also originated as partial roofs cl lncipi~nt lava 

lubes. Major collapse even" along th. chann

57. AA FLOW DYNAMICS. MAUNA LOA 1964 IH9 

/ 

I 

I 

I 

1 

I 

I 

I 

\ \ 

\ \ 

\ \ 

3 2 

\ , 

, " 

, , 

, -- 

J)) 

' ...._- -- 

---"" 

o 20 40 METERS 

'-'-----:cAPPRO=X=..-:-O~=TE-=SC::--:ALE::-----~' 

ompr•••ion of 

ch.nn~ well 

1. Initial slump end lorl 

tentlion c.ack 

2 Wedging of~well 

3. More advanced stege of 

w"'ging 

FIGURE 57.12_-~ ~dI (map view) r:l onP cI tan bow by 

~ and .Iumpng from ~ bank cI chnnd~ in tht~ 

eruption, reflecting the more stable channel configuration in this 

.,.... In tho ch.nn


A 

F1CLRE 57.IJ.-BIodascs and ~ In b.~111 channds. 1964 MauNI Loa eruption. A, Aenal VtcW J ~ blockage illong comtncleti xctor ol6ow chimnd. 

UpchaMd pond has rd.abvdy cool~ swfiKC; hotltl" mtt:nor un d draulIfIII dtM-nchannd nom below bkadc.llgt:. Ught-cnlom:lIa\'i11 a10q oPt marpl JS 1852 

~_ About 1.800-m Ind, M.ch 31. B. Acnal VloeW cl MqC (lll,uflow at blockage :wle". ~ up:hannd. About 1,650-m ek-.1ItJon. March 31. 

B 

to form flow 1A. Many smaller blockages in lk next few days 

caused overAows at this same general elevation. By April 4. 

blockages were occurring as high as 1,950 m, and on April 5 a 

large blockage at about 2,050 ft caused a major surge and overAow 

to fann flow lB. On April 6-7, repeated blockages and overflows 

at the 2.000-2.IOO-m level prevented sustained feeding of any How 

system below 1.850 m. By April B, blockages were causing many 

overflows at elevations as high as 2.300 m~ and blockages and 

overflows extended back almost to lhe venl during the next two days. 

Most debris blockages rcdlKtd. but did not stop, dowochannel 

Row; typically, lillie glowing lava was visible at the surface in the 

constricted sector of the channel, but nuid lava would continue to 

flow or at least ooze out at the Iowtt end of the constriction. The 

amount of lava ponded by a blockage could ~ large relati\'e to the 

upslope channel volume; blockages and poneling promoted construction 

of O\ouAa.v levees that in tum could be enlarged by 

spreading of the levees and O\'ernow of the entrapped ponded lava. 

The largest ponds, at the l,800-m and 2.0S0-m levels. were as 

much as 100m wide, 10m deep, and SOO m long; periodic abrupt 

release of much of the ponded lava could significantly modify the 

downstream now regime. 

A dynamic relation was established early between biockages 

and fonnation of lava boats: generation of a duster of lava boats by 

failure of the channel bank provided material to cause a blockage at a 

downstream constriction. and in turn formation of such a blockage 

would lower the dlannel level farther downstream, causmg additional 

failure of the channel bank and generation of more lava boats. 

As a corollary, when the channellC\-d was low and few lava boats or 

other debris were evident in the channel, blockages and ponding 

could be inferred to be occurring upchannel. Both straightming of 

meanders and small fluctuations in channel level. perhaps initially 

related to short-tenn variations in rate of lava production at. the vent, 

were thus capable of generating blockages farther downehannel. 

"The intensity cl such perturbations tna-eased during the first t\\"O 

weeks of the eruption, even though the rate of lava production at the 

vent remained roughly constant, at least from March 30 10 April 7.

57 1\1\ FLOW DYNAMICS. M/lUNA LOA 1984 1>41 

2500 

1500 

.Q' 

j' 

o' 

z; 

I 

1000 26 30 1 

MARCH 1984 

• 

APRil 1984 

--Vent 

® 

l8\ 

•• 

,.", 

.i' . 

.,~ 

I-IGURE 57.14 -ElevatKlM of htW-t M~ produans block.aBft (curled 

oos.tet) In main Row dwlnd of 1964 Ma&IrWI Loa eruption 

- 

10 

In lO\Ner reaches of the channel (transition lOne), surges caused 

fluctuations c:l several meten in channel level; they also affected the 

heighl and rale of deformalion of the ma~at sbear lenses adjacent 

to the channel. Increased marginal deformation dunng a surge was 

accompanied by creaking and crunching noises. The mal"grnaI shea. 

areas rose dunng passage of a surge and subsided afterward, 

demonstrating that the zone of sheanng was underlain by fluid lava 

hyd..ubcally connected to the channel. 

Flow velocities in the channd commonly increased dunng a 

surge, especially where the channd gradient was fairly uniform. 

Where the gradient flattened below a cascade, however, the effect ol 

a surge was mamly to mcrease the lava Ievd, wilh little or no increase 

in velocity. Many surges carried abundant debris from the causative. 

blockage as a ,aft that spanned much d the channel and mo\'eci more 

slO\Nly than the underlying lava. ~ cooler and more rigid rafted 

material lalded to increase the bulk Viscosity cl the lava and drag 

along the marginal 1e\'tt5; the5C interactions raised the level of Ro\\' 

within the channel and decreased the velocity of the lava. A few 

minutes after passage ci a sw-ge, exceptionally fluid lava that had 

been stored in the interior of the blockage pond typically an;,·ed in 

the channel; flow ''elocities incrt:ased. and the previous channel 

gradimb were ustored. 

LEVEES 

SURGES AND OVERFLOWS 

Lava that ponded belllnd channel blockages ..=tually 

escaped. either by ovcrflowmg the channel banks as the pond level 

,.". 0' by breaking tlu-ough the blockage to generate lava ,ul"gCS 

downchanncl. Smal1 blocltagcs commonly faded when the woight d 

the ponded Java exceeded the strength of the obstruction. At !irst, 

the dam would begin to creep downchannel, at increasln8 rates. 

\Vilhin several minutes, Aow rales would increase from a frw meters 

per mmute to a few meters per second. Then tht lava pond would 

break through a low or ....-eak area to form a surge of lava down tbe 

channel. At times. du, OCCUlTed In such volume that the I"eleased 

lava could oot be contained In the channel below the dam (fig. 

57.15~ At othe, times. the mlOg impounded lava would bft and 

Root lhe jammed debris over the constnctlon to fonn an O\'ert1ow 

surge. When the volume of the breakout was reduced by overflows 

to an amount contamable within the channel. the excess lava 

progressed down the flO'oY as a channel surge. 

Where the pond was confined behind high overlIow I....... the 

weight d the pond could bulldoze the Hank d the levee aside. 

widening the channel or causing failure of the levee. Failure of the 

levtt5, al times observed 10 opal like a giant bam door, couJd 

abruptly rdeast: a large volume of lava along the flank of the AO\" 

rather than directly downchannd. Such lateral breakout.s could 

generate major new lava tongues, such as flows IA and IB. In such 

breakouts large blocks of !e\'ee material were rafted downilope 

embedded In the overAow lava. Much of the volume of the eruption 

was dissipated In this way after March 29, causing skJwmg and 

stagnation cl the now terminus. 

Marginal levees are common ft:atures of aa flows and are 

closely ,e1aled to channel evolution (Hulme. 1974~ At Mauna Loa 

10 1984. several types of I~ formed lhat art: broadly similar to 

those described for small short-~\-ed aa flows on Mount Etna 

(Sparo and othe". 1976~ At Mauna Loa. howeve,. ia... growlh 

varied notably with time and with paso.on along the How. 

EARLY LEVEES 

Early levees on Mauna Loa are representt:d by the broad 

topogl'aphicatly hogh rubbly Hanks d the aa How (fig. 57.9C: high 

POlO" on the M-shaped p",file) thai weJ"e kft behind," the LOne d 

dISpersed How as the cenl,at wne d highest \docity How drained 

downslope to fonn an incipient channel (fig. 57.';~ In many places. 

lateral spreading of the flow tmded to displatt and cause outward 

avalanching d aa rubble along the early funned levees (fig. 57.9C) 

Thus, tht: f:arly Mauna Loa levees seem transitional between the 

features that Sparks and "'has (1976) ..Ued initial levees and 

rubble levees. Nested lateral levees also tended to form rapidly at 

MaWla Loa, inside of the early lateral levtt$, as the center ci the 

flow lhinned and mo·..ement b«ame cmcentrated along an incipient 

channel. In companson With mitiallevee.s of aa Rows on Etna. such 

early lateral I...... on Mauna Loa aa Hows were morphologically 

mort: complcc, broader relalwe to channel width. had high points 

farther from the channel banks. and formed O\'er a penod of hours to 

days rather than within mmutes of passage of the flow front. These 

difft:rt:nces .sttmingly rt:Rect the largt:r siLt: and longt:r movemt:nt 

history rl the Mauna Loa flows. In addition, on Mauna Loa the 

flowing lava between tilt: 1t:VeeS rapidly devdoped. a conca\'e-upward 

p.-olile because d ,hining d the liquid How core downslope and 

p",bably also because d effects d preexisting topography (fig.

1542 VOlJ:ANISM IN HAWAII 

A 

FleUR£. S7.1>.-Channd ow:rflows. A.~cl 0Vft'fi0w at abool 2.600-m kvd. at 1800 April 10. Blocbgchas broken. pumining ponded Lava 10 JPc.ad~ 

aol~ the channd. B. Photograph laken about 5 minul~ after thai an A. UWC" part ci overflow has ll~td and lava is draining bad inIoorilinal~;011 

~ dopes wrgc- continues 10 Rood and (ft~ channd. 

57.9C) In contrast, profiles of flows on Etna (and also those 

modeled by Hulme, 1974). which art: confined within marginal 

levees, are convo. upward. On both vokanoes, formation of early 

levees appears related to the yield strength of the lava. 

"The early levees thal formed at Mauna Loa were gradually 

modiJied by laler processes of composite levee growth. mainly 

"wolving channel overRow and d.fonnatioo of already formed I...... 

These processes produced complex: levee structures somewhat similar 

to those described on Etna-accretionary, rubble. and. overflow 

lev... (Sp..-l. and others. 1976}-although l..-ger and more notably 

composite in origin. Alllevtt growth on Mauna Loa flow-so after 

a central channd was eslablished. was caused by variations in 

channelleveJ related to blockages and surges. 

OVERF1.DW LEVEES 

The most common levee-building process was overflow of the 

channel banks during passage of surges. During vigorous surges, 

discrete small aa or ~ flows spread laterally to produce 

~ow lev... (fig,. 57.16A. 57.90. E) of the sort diagramed but 

nd observed by Spa"" and hi. associates. Weaker SUTg.. thal 

oompletdy filled the channd without overflowing caused scooaceous 

or dinkery aa to accumulate along the channel margins, producing 

rapKl growth rn lnu height by processes somewhat similar to the $0 

called accretionary levees described on Etna. ~rRow and accretionary 

l~building processes were thus rntergradational, ~ 

during a singte surge ~1. At Mauna Loa, levees formed by lhese

57 AA FLDW DYNAMICS. MAUNA LOA 1984 1543 

B 

FIGL Ric 57 15 

Contmued. 

surge-overflow processes had depositional slopes of no more than 

10°-1 So, in contrast to slopes tt 50°_8S o reported al Etna. 

DEFORMATION LEVEES 

An imporlant process. which steepened overflow levees at 

Mauna Loa, was outward displacement of overflow levees pushed 

by the increasingly deep lava confined in the channel. By this 

mechanism, overflow levees with initial surface features of smaJllava 

flows were converted into angle-of-repose rubble ridges, which stood 

as much as 6-8 m above the original channel level (fig. 57.9E). AI 

times, slabs of scoriaceous pahoehoe severaJ meters across, derived 

from the crust of the channel lava, were tilted and overturned during 

upwelling of channd lava associated with surges (fig. 57.9f) These 

features are best described as deformation levees, although somewhat 

related in process and resultant appearance to the so--called rubble 

levees described near the toes of Etna flow Fronls (Sparks and 

others, 1976} Defonnation of a levee was commonly recognizable at 

a distance by rising dust douds, as aa debris ground together and 

cascaded down the flank of the levee (fig. 57.16B~ Such outwa


A 

FfGURE 57.16.-uwa laTa. 1964 Mauna Loa ~phOl'l. A. Overflow kvC"r': channel !nd IS 1oY.. bd....·ft:Il 5lIrgrs. Sklw oYl:"l"fl


although different in origin and appearance from the accretionary 

I..... of Spark. and other. (1976~ In !he transition zooe, characterized 

by a developing channel flanked bY .Iowly moving !emshaped 

ridges of .. rubble bounded by discrete shear zooes (Iii. 

57.5~ !he initial levees were widened and en!arlled by accretioo of 

laterally moving rubble ridges. The ridges moved fairly rapidly 

during lIllJ'8


c 

Originel chenn,1 

wtlli. 

9.2m Lev•• 

Sh..t-flow I' ~>:it:\ri·~I~ -oj -6~ol~- :~··b.2r~/,-i:~- 

F~';i,;,~:,(~~~,s/:Y"'/)/;;/'7Jl~' 

Rubbll Pre-' 984 flow. 

H

57. AA F1.OW DYNAMICS. MAUNA LOA 1964 1547 

J 

o , , 10 , 11 , 20MrnM , 

FIGURE 57.18.-Posteruption profiIe5 (00 vertical aageration) across channels c:l the 1984 Mauna Loa Rows. l...oc:alions cl channel .tations tobown on bgure 57. lB. A. 

Channel. at about 2,900 m, 100 mdown8ow from wellernmoet vent. that wu .bandonedjuat .Ier initial stabilization on about April 10. S, Owmel lItatm 12, at about 

2.900 m; mature ttAle of north channel. adjacent to vent rampart. C. North Raw. at 2,85Q..m elevation. 70 mfrom vent outlet. D.


3.soo-m -enu 

SE..... Irrmia.... 

F10Ir 1 ~_. __ •••• 

Vml I, middle ••••_ 

Do.••••_. _ 

Do. 

Do. 

'Iow' 

FIo_' 

Vml I, maiD _I ._ 

\lmt I, middJe 'I'Ult 

Vmt 1, mai.a _I __ 

Do. 

Do. 

Do. 

Do. _ 

\!!:at" 

_ 

Do. ••_ 

Do. _ 

Flow IA •••__ 

~ .. -----_... _-- 

Do. 

Do. 

F1OW'IA 

Do. 

\bat" 

Flo_ lA 

Do. 

Do. 

\bat" 

••• 

_ 

•••__ 

Do. 

Do. 

•• • 

••• 

\leal I, -.in ft:Dt 

Do. 

__ 

_ 

VetIl dl&Dad _ 

Vall I, maUl _I •• 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. •__ 

Van" 

_ 

Do. ••••• 

I1S2 ftDt IUtioQ _._ 

FIcrtr IA _ 

Venl" 

•••_ 

Flow I •••_ 

vent I. main ¥eDI 

Do. _. _ 

Vetn" 

Do. 

._ 

_ 

1"2 1'ftIt ItIUoa 'hut dwuld 

Flow I 

_ 

Do. ••••_ 

Nordllow •• • 

North ..... ftIlt _ 

NorD.... • _ 

Nortb low nDl 

A 

FIO'II' I 

_ 

Nontlllow etaaDMl • 

Do. _ •••••••• 

Do.•••••••••• 

Do. _ •••••••• 

Do.•••_•••••• 

Vall 9,I46lttlioa •• 

D... 

(lIIOI'd) 

3/2l Ion 

3/2l IS'" 

3/" 

3/26 

3/26 .'" .,. 

l/26 ,,,. 

l/26 1324 

l/26 '340 

l/26 1420 

3/26 "00 

3/26 161l 

3/26 

".. 

3/27 

3/27 

'42' 

3/2, 143S 

3/2, ,>4, 

3/l7 2016 

3/27 20" 

3/27 23,. 

3/ZI 

3/ZI 

3/ZI 

.." 

",. 

1241 

3/ZI 1610 

3/" "00 

3/" 17SS 

3/10 "56 

3/10 .... 

3/.. 1230 

3/.. 1420 

3/" 164' 

3/" 0712 

3/ll IOS6 

3/ll 12,. 

3/" IS56 

3/" 

".. ".. 

,.., ",. 

'OlIO 

IUS 

"" 

'64' 

"" 

I1lS 

1012 

12.. 

"., 1411 

.... 

.90S 

1545 

".. 

IS,. 

"" 

..., 

12" 

1... 

"" 1220 

"" 

.... 

.m "" 

4/07 

".. 

,.., 

4101 lOB 

"07 

"07 I"" 

17" 

1026 

1145 

1306 

,.., 

ISIS 

IS.. 

".. 

"20 

..,. 

"" 

"" ..,. 

'500 

1500 

1610 

"" 

"00 

0.31 

.59 

.,. 

1.29 

UI 

..'" 

!.SO 

UI 

,.,. 

1.61 

..62 

1.61 

2." 

2." 

2.SS 

2.60 

2.79 

2.60 

2.9l 

'.20 

,... 

l.41 

l.61 

4.50 

•." 

S.23 

,.. 

S.S4 

'.64 

6.21 

•.'" 

•." '.60 

'.64 

,... 

1.39 

.... 

•." 

'.64 

U. 

9.l1 

9.54 

•.,. 

10.10 

10.33 

10.60 

10.60 

11.46 

12.lS 

12.16 

12.45 

12.55 

12.6) 

n.s 

U.S) 

13.39 

13.64 

1l.61 

14.31 

14.0 

14.49 

14.5 

14.S6 

14.5' 

14.59 

14.62 

U.S 

11.)1 

11.51 

11.)1 

11.51 

11.61 

11.65 

TABLE S7.1.-Lva 6ernpenUe onJ Jmsjy, 1984 M{mTtG Loo m.pion 

[0.)'1, .- • d..)'1 tr-~ 01 en&ptio.: ~. diIta-=e fr__I} 

......... 

(m) 

',500 

2,610 

2,560 

2,910 

2,910 

2,190 

2,190 

2,'90 

"'60 

2,160 

2~90 

1,'" 

2.'90 

2.910 

2,500 

2,'" 

2,'" 

2 ... 

2 ... 

2 ... 

2"10 

2,'10 

2,110 

1,610 

2,110 

2,110 

2,110 

1,310 

1,150 

2,110 

1,ISO 

1,610 

'.9>0 

2,110 

2,110 

2,'10 

2.... 

2,'" 

2,860 

2.... 

2 ... 

2.... 

2 ... 

2,'" 

2 ... 

2 ... 

2 ... 

2 ... 

2 ... 

2,.110 

2,110 

2.500 

I.... 

2,110 

2"" 2,190 

2,190 

2,110 

2,110 

2.500 

2,110 

2~" 

1,910 

2,930 

2,910 

2,930 

2,910 

",. 

2,930 

2.930 

2.930 

2.930 

2.930 

~,o> 

....... 

(km) 

0.01 

••• 

,.. 

.• 

.• 

.. 

.. 

.. 

1.5 

.. 

11.1 

.IS 

... 

.• 

.. 

.• 

.• 

.01 

." 

." 

.. 

.. 

16.50 

.• 

20.' 

.. 

14.2 

24.S 

.. 

.. 

16.5 

10.2 

.03 

.0> 

.IS 

.07 

.0> 

.12 

.12 

.12 

.03 

.• 

.12 

." ., 

.. 

.02 

••• 

." 

••• ., 

., 

11.0 

.1 

.10 

•., 

.IS 

•., 

10.2 

2.' 

., 

,., 

.IS 

.20 

.. 

.• 

... 

2.' 

1,01) 

1,121 

1,125 

1,145 

1,10) 

1,146 

1,141 

1,IlI 

1,Il9 

I,m 

I,UI 

1,1l9 

1,1)9 

1,IlI 

1,140 

1.135 

1.1l1 

1,121 

1.1l1 

1,121 

1,136 

1,130 

1,IlS 

1,10) 

1,126 

1,136 

1.... 

1,12S 

I,ll) 

1,1l2 

1,133 

l:m 

1,131 

1,136 

I,m 

1.140 

1,llI 

1,141 

1,1l9 

1,140 

1,1l9 

1,131 

1,12' 

I,ll) 

1,140 

1,142 

I::;: 

1,121 

1,100 

1,123 

1,In 

1,126 

1,011 

1,12S 

"""" 

T I B I 

T28E 

H P 

H G 

TIBF 

H G 

H G 

TIBE 

T I BG 

T2BE 

TIBE 

H G 

H G 

TIBE 

H G 

TIBG 

TIBG 

TIBE 

TIBE 

T I BE 

T I BG 

TIBE 

T I BG 

T2BF 

T2BE 

T I CG 

T2BF 

T2BF 

T I BG 

T I BE 

T I BE 

TIBE 

TIBE 

H 

G 

TIBG 

T I B E 

TIBG 

TIBG 

TIBG 

TIBG 

T I BG 

T I BG 

T I BE 

T J B I 

T 2BG 

T I BG 

T I BG 

T 1 BG 

TIBE 

T I BF 

T I BF 

T I BF 

T I BF 

TI8E 

TI B [ 

TlBE 

0.'5 

2.23 

.." 

1.01 

1.20 

1.19 

1.1' 

1.11 ." 

.60 

.13 

1.12 ." 

.." 

." 

2.' 

1.19 

1.14 

1.02 

..22 

1.01 

1.20 

.79 

1.10 

.70 

2.'" 

.51 

1.41 

..>4 

.12 

..0> 

US 

1.72 

.10 

2.S1 

1.13 

... 

J.lS 

.99 

.53 

US 

2.31 

." 

." 

1.0 

.51 

.33 

.51 

.33 

.>4 

....... 

NER-7 

HER-IF 

41I1NBI 

NER-1212 

NER-12I) 

NER-l2f13 

NEIl-IV4 

NEIl-IVI4 

NEIl-lVS 

NBlMU4 

NEll_IV12 

HER-12I1S 

HER_IVI6 

NEIl-IVI7 

HEIl-IVII 

HER-12/10 

HER-1212O 

NER-12121 

HER-IV2) 

NER-12124 

NER-1212S 

NER-IVZI 

NER-12126 

NER-IV29 

NER_IV3O 

HER-IVll 

HER-IVll 

NEW-IUJ2 

NER-l2134 

NER-IV)S 

HER_I2I36 

NER-IV)l 

NEJt.-lV3I 

NER-IV40 

NEJt._12I41 

NEIl_IV)9 

NER-l214l 

NEIl-I2IO 

NEIl-I2I4S 

NER.-I2I46 

NEIl-12141 

NEIl-I2I41 

NER_I2/49 

4/11NB3 

NER-I2I44 

NER-IVSO 

NER-I2ISI 

NEJt.-12t52 

NEIl-IVn 

NEIl-12tH 

NEJl-I2ISl 

4f1.H84 

NEll_illS' 

HER-IUS5 

NER-I2IS6 

41I1HB2 

NEIl-I2I60 

NEIl-I2I62 

NEIl-I2I60 

NER-l2162 

NEIl-12I6l 

c......•• 

Owmd aI orenl; c:oU:to't probe be_ AnKle; 

poor rud.iaI. 

~ Bow (rMt; iItlbedded 2 m in toll COft; 

'lable IS 1JIitI. 

&, C:O~ of lbecnrub Bow. 

FounWn; lripod rell, so m diliMICe. 

FounWn; uipod ren, so m dUlance, lI.bIe 

1,144-I,14S ~. 

I-m-thidr. II*ler-fed !Sow; fuled tip leVerai 

!riel. 

Founwn, uipod II 20 mj luble 1,134 

1,I46OC,~t. 

FOllal&i.a, tripod &I 20 m; Rlble 1,134 

1,146 OC, oblUftr 2. 

I"ahoeboe -eow ffHI m.U.n dwllId;..bIe 

2 miD. 

Din:cdy iD main chMltd; Igbk WgenI 

minule.. 

~ 30 m (n;a cJ.uw,1; IUlDItiD, wbm 

_. 

Do. 

_ 

VeDI I, mail! nlll __ 

Do. __ •••••••• 

'ftal I, welt nllU _. 

D... 

(mold) 

4/11 

.,Il 

4113 

4/13 

Timo 

(H,I.I.) 

17I0 

'935 

1001 

1142 

1215 

"'. 

.." 

S7. AA FLOW DYNAMICS. MAUNA LOA 1964 1549 

TABLE 57.1.-Lt.Ja lemperube onJ delJlifal, /984 M_ Loa aupIion-Conlinued. 

17.66 

19.34 

19.36 

19.42 

19.45 

19.60 

20.35 

EIontioa 

(m) 

2,700 

2,190 

2,190 

2,930 

2,9" 

2,110 

2,9)0 

DQuru:c: 

(luD) Codo' ....... 

2.6 

.20 

.10 

.OJ 

.06 

.01 

." 

1,106 

1,102 

1,132 

1,125 

1,137 

1,121 

1,122 

T2BP 

TIBP 

TIBI'! 

H P 

TIBG 

T I B I 

T 1 B I 

.n 

2.12 

.n 

... 

.57 

NER-12IM 

NER-IV61 

NER-U/65 

NER-I2ID 

NER-I2I66 

Aa ovcr6ow from maiD ehaancl, stable 2 mill. 

Dinctly ill mai.II cballad; Iltttr sp.bk:. 

l\l.bc emitted dinctly fn:m ~Ilt; __ stable. 

MIlWIl; bud beld; 20 m d.istaDCC O¥a 

c:baDDd; pool' teadilll. 

11Ibc from I)OIIlkd dwlDd; ltabIe 2 mill. 

1\abc emitted directJy f..- ftDl. 

~ from c:haaael; _r stabk. 

A 

))00 

))40 

~ 

0 

0 0 

))30 • 

• • 

• • 

on 

:> 1120 

iii 

~ 

w 

U 

on 1110 

w 0 2 • • • 

10 12 14 

II! 

DISTANCE FROM VENT, IN KtlOMETERS 

'" w 0 

i!! 

:> B '"~ 

... 

« "00 

r 

:l 1140 8°" 08 

w 

... 

° " 

'00 ~ 

° ° 

~ 

0 ° 0 

0 

° 

~ 

.' 

1130 

• ~ 0 

1120 

0 ~ 

0 

0 

1t 10O

ISSO 


long-traveled tube-fed pahoehoe flows, such as have characterized 

many prehistoric Mauna Loa eruptions. 

before the end of the eruption (Swanson and others, 1979; Moore 

and others, 1980~ 

LAVA DENSITIES 

Vesicularity of the 1984 lava was noted in the field to decrease 

downchannd. as discussed. in connection with the variations in lava 

types. Near the vent outlet, channel lava was Ruffy near-rebculite 

that had tbe consistency of whipped egg white; downflow, it became 

dense bloclc.y lava, containing only the scattered irregular vesicles 

typical of conso~dated aa (Macdonald, 1972, p. 70~ Density 

measurements on samples coUecled. at temperature sites confirm a 

downflow increase in density (fig. S7.20~ particularly for samples 

collected during a single day, and also indicate a gradual decrease in 

density of vent material during the eruption (fig. S7.21 ~ 

The increase in density of lava with distance from the vent (fig. 

S7.20A) is striking, when differing lava types are distinguished. At 

the vent, the densest values are largely for degassed pahoehoe oozed 

out from small tubes near the base rl the spatter ramparts or from 

the quietly effusive vent 4 (fig. S7.20A, triangles~ In contrast, 

quenched spatter and frothy lava dipped from the channel have 

densities as low as 0.35 g/an 3 • indicating about 85 percent porosity. 

Downchannd. samples from the incandescent cores of aa flow fronts 

are denser than those from rapidly quenched. channd overRows 

(typically 5Coriaceous aa) or samples taken directly from the mannd. 

These changes in density must rdate to degassing and kneading 

out of vesicles in the lava as it Rowed downchannel. Significant gas 

emission from the channel lava was evident in the field; SOz levels 

were so high that manned observations were rardy feasible downwind 

of tbe channel. The downchannel density changes prohahly 

contributed significantly to the decreased. downchannellava volumes 

measured in the 1984 channd system, as discussed later. 

In addition to density changes with distance from the vent, the 

density of spaller sampled at the vent decreased fairly systematically 

during the eruption, from 1.0-1.2 g/cm 3 early in the activity at the 

2,900-m vents to ahout O.S g/cm 3 late in tbe eruption (fig. S7.2IA~ 

We interpret this trend as rdlecting an increasing ratio of gas to 

magma in the fountains as discharge rate declined during the 

eruption. Temporal changes in density of channel or overRow 

samples were more subdued, presumably because such effects were 

masked by large concurrent effects of downchannel degassing (61. 

S7.21B~ 

The long-term decrease in spatter density is in accord with the 

ohserved inverse correlatino between fOWltain height and channel 

levd at the vent, which involved RuctUabOOS over intervals of a few 

tens of minutes to a few hoors (fig. S7. 22~ At the times of higher 

fountains, which yidded the least dense and most gas-rich spatterat 

times approaching reticulite-Ihe channel level dropped, indicating 

a decrease in bulk. eruption rate of lava. Alternativdy, more gas 

may have been ",solved and kneaded oot during the high-fountain 

phases, producing denser channel lava and lower channel levels 

without a decrease in discharge. Similar gmeral effects have been 

noted at seYeral eruptions of Kilauea, in which high wispy founlaining 

(maximum gas release) occurs as lava production declines just 

RELATION OF LAVA TEMPERATURE, VESICULARITY, AND 

VISCOSITY 

The temperature measurements and other observations on 

Mauna Loa lava bear signiftcantly on interpretations that the 

pahoehoe-aa transition reRects increased viscosity rdated to gradual 

downflow coooog in open channels (Swanson, 1973; Peterson and 

Tdq, 1980~ At Mauna Loa, lava temperatures varied little for 

10 Ian downstream from the vent (fig. S7.19A~ Downflow temperatures 

have been similarly stahle in aa at Kilauea Volcano (fig. 

57.23~ Bulk aa temperatures were presumably lower downRow 

than near the vent, because the ratio of Ruid melt to pasty clots and 

solid debris decreased down the active channel. Some process, 

however, maintained the temperature of tbe fluid porboo of the aa, 

and tbe hulk aa viscosity increased independently of the limited 

temperature variations in the Ruid part of the channel fiD. 

High temperatures in the aa were partly sustained by heat of 

,crystallization, as indicated by a downRow increase in microlite 

populatino (see ncd section ~ 

Frictiooal deformaboo of the melt 

(Shaw, 1969, p. S32) may also have been significant. Lava in the 

channel had the consistency of reticulite near the vent, and even 20 

kIn from the vent it contained 30 volume percent vesicles. The melt 

fraction was present in the form of vesicle walls that defonned as the 

lava degassed and flowed turhulently downchannel. Flexing of 

buhhle walls (during flowage, turhulent mixing, and huoyant rise of 

gas), supplemented by friction along margins and shear planes 

within the channel, is thought to have contributed significant heat to 

maintain high temperatures in the chamel lava. 

Given that temperatures in the fluid-melt component were 

stahle and that the slope gradient and flow velocity decreased 

downRow, what produced the observed increase in viscosity and 

initiated the downfJow transition to aa~ On April 2, the apparent 

viscosity in the channel near the vent was about I()2 Pa's; at 1,950 

m. pahoehoe channel liD had an apparent viscosity of 10' Pa,s; and 

at 1,600 m, the apparent viscosity of aa channel liD was about 10' 

Pa,s, as determined hy relatioos between flow velocity, channel 

gradient, and channel depth (Moore, chapter S6~ The observed 

increase in both microlite content and solid debris downOow must 

have increased the viscosity of the silicate fraction (Shaw, 1969. fig. 

2~ In addition, the viscosity increases appear closely rdated to 

density increases in the channel lava (fig. S7.20~ 'The density 

increases require an attendant decrease in gas and vesicle content of 

the channel lava and increased thickness of vesicle walls. Decreased 

vesicularity has been shown experimentally to increase the viscosity 

of lava (Murase, 1962; Shaw and others, 1968~ Thus, .... at 

constant melt viscosity, tbe bu~ viscosity of the channel lava would 

increase without changes in temperature or microlite population. 

Thicker vesicle waDs would also increase resistance to flexing of the 

melt, reduce associated deformational heating, and evmtuaUy allow 

a negative heat budget. 

High gas content and thin vesicle walls may, in part, also 

account for the low viscosity and high fluidity of pahoehoe.

57. AA FLOW DYNAMICS, MAUNA LOA 1964 1551 

2.10 r-.-'-'-'-''-'-''-''-'-'-'-'-'-'-'-'-' 

2.10 

2.40 

2.20 

• 

• 

• 

• 

2.00 

1.10 ~ 

1.10 

1.40 

1.20 

'.00 

0.10 

• 

• 

• 

• 

•• 

• 

0.80 

0.40 

Entire eruption 

March2li 

0.20 '_.L--'-~-L~----'~~~.L--'-~~-->"----'_~.L_..J 

2.10 r-,..--r-..--..---,-~-,--r~-,--.-~~--.--'-''''''''' 

2.80 

15 ti 2.40 

~ 2.20 

u 2.00 

• 

• 

• 

March 26 

April 6 

0.20 '_.L--'-........-L-->..----'___''---'-.L--'---L~~___'_'_.L_..J 

2.10 r-r-,-,'-''-',-,,-,~~~-,-,-,-'-'-'-' 

2.10 

• 

2.40 

2.20 

2.00 

1.101- 

\.10 

1.40 

1.20 

1.00 

0.10 

0.10 

April 7 

Apo-H 8 

0.40 

0.20 Oir.L--:2;-.L-~.,'--j.,~-j.,'-c';;0.--'-";';2----'-"~'-->"-'1~ • ....J Oir.L--:2;--.L-~.,'--j."--j.'~';;0.--''-c';';2.--'-''~'-->''-'I~ • ....J 

DISTANCE FROM VENT, II' KlL.OMETERS 

EXI'IJ\NATION 

Type of ..~ ..mph: 

D S~".t • Pehoehoe 

• Ch-.I II{ M co.. of 

oOYeffIow ~Iow 

FkuR£ 57.20. - 

Mcasuud lava density plotted apml dislalll:e (f'OIQ the venlI, 19&4 M.una Loa eruption. I>.ab. •.hown for individual d..:es as well as for 

entire~. are from ,.bIe 57.1. All smapIes were coIkded no. and qumchcd in watel'. Densicy was determined by ~.1nUMR"C

1552 

2.80 

2.80 

2.40 

2.20 

2.00 

1.80 

1.80 

1.40 

'" 

w 1.20 

Ii; 

1.00 

1= 

'" 0.80 

ili 

u 

0."" 

ụ. 

:> u'" 

0.40 

0.20 

Ir 

2.80 

"' 

2.80 

:'" " 

2.40 

~ 

,: 

2.20 

.. 

0; 2.00 

z w 

e 1.80 

1.80 

1.40 

1.20 

1.00 

0.80 + 

0.6C 

0.40 

0.2 0 

o 0 

o 

o 

o 

o o 

o 

Spatter samples 

o 


o 

Channel samples 

2 4 8 8 10 12 14 18 18 20 

TNE. IN DAYS FROM BeGINNING OF ERUP'TlON 

30 

2. 

2. 

"' 

2' 

'" w 22 Ii; 

'"~ ,. 

~ 

e 

,. 

,; ,. 

'" e '2 

!< '0 

.. " • 2 

00 

20 40 

l1ME. IN MWl1TES 

FIGURE 57.22.-Varilllic.l 01 "'va IewI in ebannd wnus beilht rl the fountains. 

the maia waL Dab obtaiMd arouDd 1200 OD April 2. 1964. Fouatain lk-iPu 

wen visl.WIy estim.tcd by rd'cr-mcc to ~cd basht of~ rampart. 

1150,---r--,----r--,---,---,-----, 

11;"' 0 

.2 

D~ 0 

~a 1130 

C"' 

n"'w 

1110 

:4- 

0 0 0 

~~ + 

• + 

1090 0 1 2 3 

• 

5 

• 

7 

DISTANCE FADM VENT. IN KILOMETERS 

FIGURE 57.23.-Temperature plotted asaimt dUtante 01 tr.vrd for Kilauea .. 

Rows from tne 1963-84 east·riEt-zone ~ioas. Plus. sample from phue 9. 

southeast b; square. sample from phase 16. southeast Bow. 

80 

FIGURE S7.21.-MU5URd bva dcmity of spillet' ....pks mel cha.oad samples 

plotted -eamt time. Dat. an: from table 57.1. 

Pahoehoe is more vesicular than aa, and retarded degassing in lava 

tubes may delay the transitioo to aa, along with the insulating role


lava: the faster the Rowage past the th('.fiJI()Couple, the larger were 

the lava shealhs. Second, thermocouples were carefuUy prthealed 

prior to insertion, particularly whm measuring Acrwil13 lava, yet 

probes in Rowing lava accumulated a sheath while those in motionless 

lava did not. We infer that the lhermocouple stretches and br~ the 

gas bubbles in movlng lava, inuu.sing the bulk viscosity of the 

adjacml melt and making additional rodt available to adher-e to the 

probe. The growing surface area exerts additional drag 00 adjacent 

mdt, hastens bubble breakage, and causes faster accumulation of 

mdt on .he sheath. 

LAVA CRYSTALLINITY 

Increases in crystal~nity affected flow rheology of the 1964 lava 

both lJ\"ef time at the "'ellts and. during Row down the lava channel. 

Three discrete textural populations of crystals are present: (I) sparse 

...esorbed phenocrysts or xenocrysts of magnesian olivine as much as 

5 mm in diameter; (2) dusty micro~tes less than 0.01 mm in size; and 

(3) microphenocrY5ts of augite, plagioclase, and olivine commonly 

0.05-1.0 mm in length. 

The sparse olivine phenocrysts everywhel"e are less than 0.5 

percent of the lava, did not vary in abundance significantly dunng 

the eruption, and are intel"pl"eted as di5equilibnum crystals that wel"e 

pl"e5ent in the summit magma reservoil" befol"e eruption. Micl"olites 

are absent in vent spattel" and become inueasingly abundant in 

quenched downchannel samples; they recol"d late groundmass crystallization 

of the lava as it flowed down the channel. Such surface 

crystallization of channel lava is probably largely responsible for the 

observed progression of flowage zones (fig. 57.51 but it seems to 

have occurred uniformly throughout the eruption. In conlrast, the 

content of microphenocrysts in quenched spatter increased strikingly 

dunng the eruption, hom less than 0.5 percent of the lava during 

initial summit activity to as much as 30 percent during the waning 

eruptive pha... (figs. 57.24. 57.25A~ Microphenocryst size 

increased concurrently with ahundance (fig. 57.25B~ although the 

precision of measurement is lower. Microphenocl"yst size and abundance 

~ncreased rapidly during the first few days of the eruption. 

slowed during the subsequent two weeks, and increased slightly 

again late in the eruption (fig. 57.25~ Large changes occurred 

within a few houn aftet'" beginning of the eruption on March 25, as 

the ~nts migrated from the summit region downrift to the 2,900-m 

level, but the abundance and size of microphenocrysts continued to 

increase after the main vent site stabilized. lhese changes occuned 

in the lava befol"e its eruption, as documented by quenc:hed spatter 

samples, although the same microphenocryst populations are readily 

recognized in downchannel samples despite additional crystallization 

of micl"Olites during surface flowage. 

During these changes, bulk major-oxide cOffipo$itiom remained 

constant virtually within analytical uncertainty (table 57.2; Lockwood 

and others, 1985~ llUs compositionally uniform 1984 lava is 

in marked contrast to lava erupted during Kilauea rift activity 

(\\light and Fiske. 1971; Garcia and others. 1984) but is typical 

for Mauna Loa rift eruptions (Rhodes. 1983~ 

Most microphenoc:l"Ysls in the 1984 Mauna Loa lava occur as 

skeletal. intergrown. and radiating hlades and plates (fig. 57.24~ 

including elongate, cored, and swallow-tailed shapes that are typical 

of rapid crystallization from undercooled liquids (Walker and oth· 

en. 1976; Lofgren. 1981 ~ Such undercooled textures are especially 

prevalent in the phenocryst-poor lava of early eruptive phase!; late 

eruptive phases have texlures indicative of more pr~onged equilibrium 

cry$tallization. We attribute: the growth of micl"Ophenocrysl$ 

characterized by wxJe...cooled textures largdy to separation of a gas 

pha5e during the eruption, not to a decrease in magma tempe...atures. 

Observed el"uptive temperature$ remained con$lant at 

1.140±3 "C (fig. 57.19B~ which is 20-30 "C below calculated 

liquidus temperatures for most phases at one atrnosphel"e (olivine 

I. 186 "C. plagiocl"", 1. 169 "C. and clinopyroxene I. 146 ·C. all 

± 15 "C; method of Nidson and Dungan. 1983~ 'The observed 

lava tempe...ature:s would approximatdy coincide with the liquidU$ if 

the pre-eruptiv~magma contained about one per-cent volatile content 

(Yoder and TIlley. 1%2~ A pre-erupti,,,, volatile content of about 

0.5 percent has been calculated from gas data for tholeiitic basah 

from Kilauea Volcano (Greenland and others. 1985~ and about 

one percent volatiles is the estimated average for tholeiitic basalt in 

general (Haggarty. 1981~ 

The virtual absence of microphenoc:l"ysls in much of the lava 

erupted early on March 25, follCM'ed by increa$es in the number and 

size of microphenocrysls (figs. 57.24. 57.25~ suggests that the 

magma reservoir below the summit wa$ initially sufficiently pres 

$UTized by volatiles to lowe.. the liquidus temperature to about I, 140 

°C, thereby inhibiting crystallization. \Vith depressurization of the 

magmatic system beginning at on5et of the eruption. separation of 

gas undercooled the magma without actually lowenng the ob5erved 

lava temperatures, thereby inititiating precipitation of microphenocrysts. 

Degassing at the summit besan at onset of the eruption 

and was later focused at the 3,550-m level, uprift or the acti~ lava 

vents (Casadevall and others. 1984~ 

Even slight undel"cooling can have profound effects on the 

nucleation and growth rates of crystals. At 20-30 OC of unde..cooling, 

cl"ystals in basaltic melts can gl"ow to sizes of , mm within 

periods as brief as a few hours (Kirkpatrick. 1976. 1977~ 'The only 

alternative to growth of microphenocrysts during the eruption-a 

zoned pre-emption magma chamber-seems less able: to account for 

the compositional unifonnity of the erupted lava or its uOOercooled 

quench textures. 

The volatile: loss needed to initiate crystallization may han 

been small. Before eruption, basaltic magmas in the shallow reservoirs 

beneath the summits of Mauna Loa and Kilauea are be~-ed. 

to contain


A 

B 

c 

, mm 

D 

FIGURE 57.24.-flw:ltomiaograpbs (pbnc light) d 

rept'uentalM ~ U 1964 M_ Loa I#a, ~ progressM _reaM! in Uu: and abundance' d 

miuoplkilOU)5U with time. Miuopl........ijlb arc dear rttlanPes; circular fcal.ura arc gilS bJbbks (~). A,~at about 0145 (H.I.L) (rl Marda 25. 

SpMtcr from~ tide c:ll949c:one. al4.040 m. Samp&e MOK-l;04 pcncnt phmocryw. 0.05 mm in aYmlBckngth. 8.~at about 05IScn March 

25. ~ from ~ ncwtbeasl rift UJf"Ie. 613.650 m. Sample NER 5; 3.5 pn'Cmt phcnocrysu, 0.1 mm in aw:ragc length. C• .5arnPtd at about 1750 on March 19. 

Pahoehoe from perched pond at 2,820 m. Samp&e NER 12123; 21 pcKCIlI~ 0.3 mm in a~ length. D. Sampled at about 0945 on April 14. Otannd 

overflow near 2.87O-m vent. Sample NER 12/66; 295 percent pbcnocrysts; 0.6 mm in awerage Length.

57. AA F!DW DYNAMICS, MAUNA IDA 19&4 

Ar---,--,--,-.....---r--.-+- '-,---,--.--,--,--r---,--,---,-...,-.--.--,--,--, 

I 

30 

I;;; 

2. + 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

/HEft 12," 

o 0 

~MOKl 

°262527282830 

, 

3' I 

I 

I 

o 

2 

o 

3 

7 • • 

• • • 

APRil 

10 

11 

12 

13 

,. lIS 

o 00- 

o 

o 

00000 

o 

o 

o 

o 

o 

00 

o 

o 

o 

00 00 

o 

o 

00 

00 

00 00 

o 0 

o 

o 

o 0 00 

o 0 

0.2 

o 

ooסס 0 0 00 

o 

o 

000 

o 2. 

2. 

27 28 

MARCH 

2. 

30 

I 

31 I 

2 

3 • 

7 • 

• • APRIL 

9 

'0 

11 

12 

13 14 

,. 

FIGURE,7.25.-Qanwes in ~bundancc and size of microphenocrysts durincl984 uuption. Samplo ilhntratcd in 6aure 57.24 ate Kkntified. A. Chanses in abundance of 

mKrOphmocryltl. Plus, datA from petrographic point-c:ounting of thin KlCbons; dab. v$ial estimates of March 25-26 sampla containinl!; only ~.nc naU 

mierophenocrysts (\en than 0.15 mm in aver-age length} Values arc bdieved accurate 10 within 10 percent; a m.;Or CiIIUK cI uncertainty i. in estimatint: are.s 01 

microphenocrysts KnaUer in diametcr than the thdnes. of the thin ICdr.on (0.03 rnm} AU samples arc quenched glassy spatter or ch&nnd overflow. About one-hd the 

originaUy collected sampfes of spaller wer-e too l'oiculill to measure. B, Chanaa in size or microphenocrysts. Median lengths of plagioclase microphcnoaysts (about onchalf 

the muimum length) were otimatcd visually from t!Un sections. by reference to a calibrated kale in the microscope ocular.


TABLE 57.2.-Major-e1ement c~itiO" of the 1984 Mwna Loa louo. from 

X-ray }1JJorelUnce analyseJ 

(IndiYidul samples. ~ 10 be npraentlAM. are~ in table 57.1 and ilustrlted in 

fip-e 57.24. All ya.e. are in wricbl pauol. Total ifoa Iittcd AI Fe,o,. UncertUlly II 

awr..it pb 01' minus _ UDdard dM.tion. o.u~by J.M.lUIodet: tee l...ipmaa 

and aDen, 1965J 

0.., ------ MlIKb 25 March 29 April 14 Entire omIption 

Time ______ --- 

0145 0515 1750 '1'

,7. AA FLOW DYNAMICS. MAUNA LOA 1984 1557 

0lI March 28 is somewhaI un


TABLE ~7.3.-Dimt:tuions 

and c1raracteri.ltia of laua channeU and their changu UJidJ lime, /984 MQU1tIJ Loa eruption 

[1...oaIDsJ c:J.amd~onf.preS7.1B. Diol:ance, ~JlIleaIIlI'inspom..lIione:ebund bank.. Ikplh.~;...., lStf«ddW. PWL. Pet« W 1...iJman; NCB, NormIlII G. B....] 

H.." 

-~, (mold) 

""" 

(H,u.) Condition 

------------ ll31 1130 atable 

------------ 3/31 1200 .~.. 

, ----------- "tOI 1200 

• ......_----- 41" 1100 

, ---------... 41" 1200 'wi 

6 ------------ 4102 1230 low 

------------ 41" 1520 ... 

....._------ 41" 1550 

------------ 4f03 164' .""" lUCie 

10 ----------- 4104 13S0 

11 _._-------- 

.- 

41" I.,. ltable 

12 ----------. 41" 15,. 

Il ------.---- 4104 134' 

"".. 

1. ~'" 

----------- 4104 I'" Ihbk 

15 -_.._------ 4104 1S00 

16 

17 

II 

_ 

3121 

3/21 

mO_B3S 

15JS-I60S 

St.tioa 

Diatucc Time VelocilJ Wlddl Depth Flow rate 

(m) (a) (mil) em) (m) (10' QlJ,.) 

StatioD 1: Lower~ lA. d~ l,6OIm 

18 19 0.95 24 S O.410} 

18 22 .82 24 S .3SS 

1. 28 .64 

l' ,. .60 

" 

l' 

60 

." 

40 6 

.40'} 

.335 

.m} 

.120 

110 

l' 

.1' 40 6 

140 .18 80 .'1 

90 .28 " 

163 .IS 50 , .BS 

Stmoa 

" 

2: Uppu c..... lA, defttioa 1,7DO DI 

.33 50 .450 

,. .'0 50 .2"l .150 

l' " 

., 

15 40 .• .170 

.6 .270 

" 

, 

l' " 

. 170 .'901 

.'64 

-, (mold) 

57. AA FlDW DYNAMICS, MAUNA LOA 1984 

TABLE 57.3.-Dimmsions and cht.octaUtia cI £W cltame4 ontl tlteir cltanges lDidt lime, /964 M_ Loa nvption-CodinucJ. 

D... 800' 

""""'" 

T. Vdocily Widtll 

Flow ~. 

(H.•.I.) CcmditioD. 'a) ,.) (mla) 'a) 'a) (10' mtlfh) """",",,, 

" ".. "'" 

" ".. 

1130 

36 ___________ 

"01 

37 ___________ 

,,'" ,,,, 

s--.4: Uppu PowaIiIIe...(aile 4,..l&)...... ~_. 

24 14.9 I.' 30 ,.52'} N_ lwiGa,~ amlk: radI::E.~ 

24 14.9 I., .. .'20 ~bdow t _. 0--1 ben 

Iacrill':,~...::::r:.":.i-t ud 

mlpCy. GndieM~.~ b)' PWL UMI 1: 

NaI. 

"""" 

SUtioa 5: New......,... Ie), eIetaIiM 1,951. 

10 I.l 10 

, 

271l Statioo. is 00 dwmd=.,IMUt allna, jlJA bdotr 

''''' " 

ClllftDlly mot( flCti~ • ud brakour _ It 

about 2,000 •. GndiCDt about ZS.~ by 

P'WL ud H. Moon:. 

" " 

20 

1559 

1.1 10 .•90 Ma.y-.s: difIca11 to -ate.._,. 

~.bat~tbuW.~ 

=~iZ:::by PWLm:rii.i:::e. 

~ 6: Maia e:a-.l...........1.1•• 

- 

30 4/07 

" ,,'" 

1120 "'" diu ..... 20 10 22 

••• , .7'JO ua. Measw-cd by ad H. Moon:. 

sa..- 7: 1BS1.............2.JIO. 

40 _____ •___•• 

16lO 20 '.7 4.23 

"" 

" 

41 20 12.' US 

.42, } ~·~lt8.Moon:· 

42 

".. "" 

" , .US 

1310 

II '.1 22 

, 

,.720} Stable clwmel, carn:a~tabaft JUPnt)lClllClq 

1.15 Abo¥!: lbabest UCII 01 bIocbees, ~ kiJdiq.-.d 

~. Gndieat about .. 05 . Meuaud .". PWL, 

20 •., ••• " 

43 ___________ 

lile A ., 

I.' ,.. 20 

• ....} M-.red 9dodtiel oa ..u rnp.a.m iD. CUlU 

... ----------- 

"" 

.... lice B .. 

4' ___________ 

"03 .... sice A ., 1.7 ,.. 20 

• I."} 

No clwlF nideal. M~ bJ PWL, J. Fink, aad 

46 ___________ 

"03 ..20 site B .. 

47 'flu3 ..50 .... B .. 

.. ".. 

lilc B 

..'" .. 

.9 ___________ 

"., 

1415 site B .. 

" ".. 

4/.. 

"'" 

" 

52 

53 ___________ 

"'" 

54 _.~~~~~_~_~ 

'/09 .... 

"" 

".. .... silC 

site B .. 

sitcB .. 

1625 shc B .. 

B .. 

" " 

Staliolll: I8S2 _. eIe¥atioa 2,510 • 

7.' ,.. 20 

• I." dwlDeI. Grsdinl AI: au A is 6'; at siu: B, ".S-S·, 

Meaum:I b)' PWL, J. 8~Bub, J. F_. 

ud H. Moore. 

7.7 ,.. 20 1.50 H. Moont. 

• 

7.5 ,.. 20 1.54 No chop IiDcc ....-aiq. despite rqxwtcd~t 

iaaasc ia~uctioclnlC " 'fCSIt. Mas by 

P'WL aDd Fink. 

7.' ,.. 20 l.55 NO~Icbaqc. Mcasum:I by P'WL. T. Neal. 

• 1. Fmk. 

7.' 

,., 20 .... No c'-le siDce prcvi_ day. Mcasved by PWL aDd 

H. MOOft. 

7.' ,.. 20 1.50 Sarf80e dWlDei KtUaIIyoaly 10.3 m wide, bccmIC of 

CI'UStiDa: of marJias. Mcutlftld b)' NGB. 

7.' ,.. 20 1.50 No dwlf' a1tboufh lnd of ctwmd • .cal reponed 

dowD m. Mcuurcd by P'WL ad T. Neal. 

7.' ,.. 

" • I." Appal'CJll ~~~. ffOCll~ atimMed 

width of c CIlullcd by cnstia•• but Ian 

k~contiaua 10 low "owly UDder ctIISt. 

by PWL aDd H. Moote. 

1•.2 

'.1 ••• • 

.315 Surt'tloc is much payer aod bD DIOl'e SCUJIl IMD OD 

(/6. VoIWIIC is 00.1.,. .bout bIl£. pea. GndicDl 

3.5". Mcuurcd by NGB. 

Static. 9: MitIcIe~ ......2.780.- 

I., 

0.2lS Broed shlllow sheet-low cbtoocJ. the middIc of tIarcc 

" • CWTCliltJy kti'fIC voad tbc wesl side of 'IeDI: al 

2,790 m (Puu 9,146). Maaurcd b)' PWL ucI M. 

....... 

s..mc. II: N'" daaDDel, eJnalioa 2.790 a 

" ...__.._._. 4/09 '600 22 30 0.73 I , O.IOS 

56 ___________ 

.'10 

57 ______ ~____ "'" 

N'=b~:-~==-~IIow. 

~ by PWL aDd M. RlMldca. 

20 20 .100 Ea~ .dochy; clwlDcI. 011 ''O'UIF 1-2 m 10'lI'CI' 

• lbaa~ Measured by PWL. 

.•90 Mcutlftld by B. 

411I 1215 10.1 

" I.' " 

.1Z5 

• - tF:: by - 0'0'CI'I0w. Mcau by PWL 

51 __••__••___ 

59 ___________ .112 .200 S&c.dy 

.. 4/" 

" "" 

./IZ 12lS ..... .. .. 1.1 

" " ... • .m) JIl$! IIpIIope (10m SUlUoa of prnious=- .hich is 

_ • Fodor. 

St.Iioa 11: \Ut CMdIet. eIefttioa 2,1S1a 

.., 21 

" 

.... flow fIlC is 1.5x 106 Ib Icss tbaa OD .102. Tbac is 

aD totitbctic rdtlioa. bctwecll fountaia bciFl ..4 

cbulu:IIC'OCi;.~ Coutl~clwlDcl ~ 

Nt is 5.2x!06 m] . MeMurcd by GB. 

1130 50 1.7 17.8 U.5 

• .." ~~ ~:.;.=:"~~.about 70 pcteaIt.. 

IOlO .. 

" ".. .... lO 

• " 

20 .., a.:=:~~ (fOCIl ./04; ¥dodl)' 

.. 4/00 

.. " 

4/09 

4101I 1l.5 50 4.65 6.45 21.5 I." 

" S~~~,:::m:_~(~;~~ 

by NGB. 

'600 20 10 30 .•" CbuocI mucb slowa thaD. ia momi.. Velocity 

CRimltcd br NGB. 

4/09 '040 

17 "-"".,. 

biper ••• .m} ClwaDcI COGWDS 'Oiscous IOPJ' r-bochoc. 

1150 .. '.2 , .•50 P'WL ucI M. Rbo


6.0 

--------------~-~~~~~-~---~ 

" 

\ 

\ 

\\\\\\\\\\\\\\ 

\ 

'.0 

EXPlANATION 

CHANNB. STAroNS 

c.. runbe" In Ub6e 157.31 

x 

+ 

* 

Low. chennel 1A 

2 UPS*' chenntl 1A 

3 low. Po¥*'I.... AGed 

.... 

2 

3 

• M............. 

7 18152~ho. 

1852 YWlt 

MkId.. chen,.1 

• 

'0 Nonh chenn" 

" 

V.m outIM 

12 Weet Ylnt 

----Jl.=10:21$O 

----!!»........ 

" , 

\ 

\ 

, , 

\ 

\\\\\\ 

\ 

\ 

\\1\\\ 

1. 

25 28 27 28 29 30 31 

MARCH 1984 

----Flow 1 

~ 

0 

8:2&00 m • 

4:1930 m 

\ 

.. 

\ \ 

, I 

\~ 

\ \ 

\ \ 

\ \ 

1 \ 

\ \ 

\ \ 

\ , 

\ I 

\ \ 

\ \ 

\i 

\t;' 

\ I 

,, 

\ \ 

\ \ 

\ \ 

\ , 

9-10:9160 m 

EE 

2 3 4 IS e 7 B 9 10 11 12 13 

AJlIIIIL 1984 

1------Row lA----.~~-f 

RIIPid upflow atqMtion--- 

FIGURE 57.26.-Owmca in channel disdause with time. 1984 Mama Loa eruption as measured at channel stations (identified by IllIDber; see table 

57 .3~ Solid lines conned repeated obtervations at indindualli&es; dashed lines an: interpreted tratds for dischar1u based on data aI other station, 

and qualitali..e observabcm of c.hanneI emution.

j7 AA FLOW DYNAMICS. MAUNA LOA 1984 1561 

(fig. )7.26). Additional faclors came mto play during this time 

interval to cause stagnation of lite Row and channel system, and these 

factors may also have had a role in the early stagnation of flow 1 

bela," March 30. 

Lava temperatures at the vent remained nearly constant 

lhroughoul the eruption. as did temperatures of the most fluid parls 

ri Ihe downchannd flows (fig. 57. 19} The 1aller is thoughl 10 have 

resulted from the heat of microlile cryslalliz.ation and from thermal 

feedback associated with deformation of the silicate mdt fraction 

during downchannel Row. Despite the unifonn eruptive temperature 

and chemical composition. the proportion of solid and pasty material 

(reflecting greater groundmass crystallization) gradually increased in 

lower reaches of the channel system, raising both the bulk viscosity 

and the yield strength of the lava. Even in the zones of stabilized and 

transitional flow, increased downAow sluggishness in the channel 

indicated progressive increase in viscosity of the fluid matrix between 

the solid and pasty material. These downchannel effects must have 

been caused by changes in some intrinsic property of the lava other 

than decreasing temperature. Decreased gas content and increased. 

groundmass microlite crystallzation seem the most likely candidates, 

as discussed earuer in this paper and as previously suggested for 

basaltic Rows in general by Sparks and Pinkerton (1978~ 

We infer that decreased gas contenl played a large role, 

because fluidity of the flow appears to be at least in part related 10 

Ihe ease of deformation of the silicate liquid that constitutes the 

vesicle walls. The 80-90 percent decrease in vcsicularity of lava in 

the channel from the vent to the zone of dispersed flow and the 

accompanying proportional increase in vesicle wall thickness of the 

silicate melt may have increased the bulk viscosity by several hundred 

percent. 

The greater numbers of microutes downflow must also have 

increased. the effective viscosity of the channel fill, much in the 

manner that the increased microphenocrysl population in the erupted 

lava raised the viscosity of the lava at the vent. Degassing and 

crystallization influenced the viscosity and thus the behavior of the 

lava in differing ways. Degassing of the lava flexed the siucate uquid 

to produce thermal feedback, adiabatically cooled the lava, and 

increased the proportion of viscous siucate liquid present. Crystallization 

heated the lava but also increased its bulk viscosity. The 

combination of these effects apparently reduced the rale of flow at 

the vent, delayed temperature decreases downflow and probably 

also in the lava conduit, produced. the conditions required for the 

pahoehoe-aa transition, and ultimately contributed to the maturation 

and stagnation of flows during the Mauna Loa eruption. 

A further process possibly contributing to stagnation of the 

flow system was maturation of the channel structures with lime. 

Solidification and increasingly britlle behavior of the channel banks, 

deepening of the channels by levee growth and possibly by erosion of 

the channel floor, and crusting over of channel margins and eddies 

are among the unidirectional processes that could have helped 

destabilize the channel system during the course c:i the eruption, 

regardless of changes at lhe vent. Such maturation processes could 

have caused greater fonnalion of channel debris. initially triggered 

by small fluctuations in vent eruption rate, that led 10 lncreasingly 

larger debris blockages, overflows, and surges downchannel. 

Deviations from simple correlations betwem length of lava 

flows and eruption rate (Walker, 1973). which have been demonstrated 

for Hawaiian flows (Maun, 1980~ may largely result from 

the superimposed effects of variable vesiculation, density, undercooling, 

and crystallinity of the lava. Increased undercoaling and 

crystallinity, decreased vesicularity, and associated Inc.reased density 

would all promote higher effective bulk viscosity and yield strength in 

basaltic flows, causing transitions from pahoehoe to aa and reducing 

the length of flows at any constant eruption rate. In contrast, longlived 

eruption at liquidus temperature would promote transportation 

of pahoehoe in lava tubes, permitting lava flows to travel farther. 

The rheology of la\'3 erupted as gas-rich foam (reticulite, in the case 

of Hawaiian basalt) that deflates during emplacement will be 

markedly different from thai of degassed lava; such contrasts may 

extend to highly siucic compositions (Eichelberger and \Vestrich, 

1984~ Proposed simple correlations of viscosity and yield strength 

of lavas with chemical parameters such as silica content (Hulme, 

1974) are also imperfect (Moore and others, 19781 perhaps in 

large part because of the complicating factors just listed. 

t mally, it should be noted that the evolution of the 1984 flow 

system was similar in volume, duration, and eruptive style to several 

previous historical (since the mid-19th century) rift eruptions of 

Mauna Loa. Field and phOlogeologic ~nation indicates that 

patterns of upslope stagnation of the distributary channel system 

characterized many of these earlier events, including the 1852 and 

1942 flows that are adjacent to the 1984 flows. Sparse petrographic 

data indicate that other major historical rift flows (1843, 1926, 

1935, 1942, 1950; northeast rift samples collected by j.P. lockwood 

and G. Lockwood) also show trends of increasing content or 

microphenocrysts during the eruption. Similar observations for 

prolonged summit eruptions, such as those of 1940 or 1949, would 

be particularly significant because they could permit distinction 

between the effects of depressurization c:i the swnmit reservoir and 

degassing along the rift conduits. Additional studies of the relations 

between eruption style, flow evolution, and lava crystallinity of 

earlier Mauna Loa eruptions are in progress. 

More extensive observations are needed on the interrelations 

between gas content, crystallinity. eruption temperature, and viscosity 

of erupting basaltic lava. Changes in lava discharge rate, 

temperature, density, bulk chemistry, and abundance of microphenocrysts 

were key determinable parameters for the 1984 eruption 

that should be monitored closely in future activity. Such studies may 

answer some remaining questions: does lava temperature commonly 

remain constant during long-lived eruptions, even during periods of 

declining discharge) Does density of spatter typically decrease 

during an eruption) Does the development of lava tubes and longtraveled 

pahoehoe during prolonged eruptions require eruption 

tempeIatures near the one-atmosphere liquidus, or at least retardation 

of major degassing and attendant undercooling before eruption} 

If eruptions of undercooled lava, marked by increasing microphenocryst 

populations. can be shown to generate aa flows dose to 

the vent, observations of lava temperature and crystallinity can have 

important impucations for assessing volcanic hazards during early 

phases of major basaltic eruplions.


A 

FIGUIlE S7.27.-Upper- channel system of Row I, as~ from l'alt at 2.7lXl m (Pull 9.146 fI). approximatdy 4 km from the activ.: vent at 

2,900-m elevation. A. At 0900 on March 26. Olannel ballad Raw I Me full or overflowing: small bright specks 10 right of acli~ d"lnnd 

arc areas of still-glawi~ lava that indic.:alc a J~ ~flow within the previous hour. Small mannd of Row 2, fed by law (OWltains. is visilJe at 

UPpeI" left. Discharge (nonnaliud 10 densiry 2.0 wan') Nlmalro at 1.0 X 1Q6-1.5 X 1()6 m'/h. B, At 1600 on March 31. Lava confined 

complt:tdy within chan~~ bank,;: ~a1 forlu of till': channel and inkn'ening islands ha~~. Despite 10Wtt" channel kvcl, compar«!to 

S days earlier. fountain height is lugher, probably reflecting a higher Pfopoflion 01 ~Ivoo gases. Discharge (normalized 10 density 2.0 vJ 

em') estimated at 0.5 X lQ6-0.6 X 1{)6 m'th. Prominent spatter ramparts in left distance mark venls £01" Rows 2-4; these: grew raptdly early 

in the eruption but were Inactive after March 27. 

B

57. AA fLOW DYNAMICS, MAUNA LOA 1984 

1563 

A 

B 

FIGURE 57.28.-Changes in founlam ~t and lava production. as sem. from \'ttlt ootid (channd itabon II) dunng 1964 Mauna Loa 

eruption. A, Ai>!"ll 2: Vent founll.lni aboul 40 m lush. wdl above tl't spallle'" ramparl. Fluffy channd lava """itS IllOVIIl& at aboul60 kmIh, 

With a dISCharge rate J about 4.5 X I()6 ml/h (table 57,3, 00. 60). In oonInut 10 the ~= portions J the stabk-


TAOU 77 4.-EJIimokJ Jaily low production roles wvI {urnulalit.>e ooItJma, 

1984 22. 

MOOflll UxJ eruptIOn , .d· 

4/1 9.' IS&.9 U'5( 

./2 .. 

0 

9.' 168.5 ~ 

.13 .4 

••• 

178.1 :> 

4/. .. 187.7 

p 

, u 

.IS 

• ••• 

197.3 , z 

0 

'/6 •• .. 206.9 

, 

;112 :" 

417 .J (1.2) 7.2 214.1 

, 

4110 .07 (.28) 1.7 121.8 4/11 .05 (.20) Il 223.0 4112 .04 (.17) .7 12].7 :> 

4/13 .02 (.011) ., 124.2 

, ~ 

0 

"8 .16 (.65) ,.. 217.7 

, :> 

41. .10 (.,w) 2.4 220.1 5 ~ d 

~ we 

4114 .00 0 224.2 

• > 

w 

~~9 

I Hourly rrodUUlOIl nfn lor earl) utll'U()1lS hom Illmnul tOI JU--075(), l'lS) aDd upper > E· 

nh ZOlW (0Y00-1700, )12S) ~_d by an:. aDd Ih,,~ me.Uil'ltI("nl. UP. l.ockMlOd. 

....nllet\cOOllnun.• 1'JS4}. Summll"" 15 mor.t1y Lhtll)' ~~ ',nl.....,d ~rw&rlkn.Lity, I.S 

ltCI'll'). W Wllurnt' II n:duccd by • third \0 IN.M COffipenbk 10 YOlumt nllllVlelI f~ linn :I 

fl1lrt"..f'U1&4 (nlillllllfd Iveragf dfnsul' 2.0 1I:rn1I). 

2. ourly productIOn ",1~ fot finl" h o(nuplioo frOID l.900-m ,,~nt 11..1 (1600 .HZS to :> 

:> 

~~~~76.~ICI=:~ ~~lIl~==f~:.n:~~~t:a~~~I~~d':"Oll'i I~~ 

U 50 

Ull(TvaI. 

J. Prndun100Q rIl~ dCI~ from Cban.l!clllXDurft1lUIlIll 1,800 to 1,9OG-1II ola.l_ 

(lat>ir S7 J). Eo.lil:::PIfd I'~ dmwl), 2.0 a/crn! 

"' 

7 

0/ 

:> :if 

.. Prodl.K1J011 1'aI~ InlnpoWfd bn~n nth; r.... r""'IOUA ud lubKqUC:OI daya 

¢ 

S. ProdOCliwl rllf detutJUocd IrOlJl channel mruurnunm aI 2,SOO fO 1.8SG-m UlllOlU 

(Iltok S7 J).. EI,umllro ."tnagt' dtnnty, OS II eml ; ICcordil1llly, obof~d diM.h~ (io 2. pvtnlhcsu) .re nducetl by Ihrtt-tjUltlc,.. In ll1lIkc UllflflIl'lIble 10 «her mnlll«~nn d 

6. End of ~1\lrUon 

? 

"'f 

I 

25 3D I' lD 

MARCH • APRIL 

•! u• 

o 

, ~ 

, I 

Preeruptive degassing; 

~' 

abundance and size of ,," 

mlcrophenocrysts ;;-' 

lava temperature 

\ 

---------------------------------.. 

end composition 

\ , , ,, 

" 

----- --- 

Discharge rate; " 

leva den.ity 

, , , , , , 

" 

2. 30 

• 

10 ,. 

MARCH 

APRIL 

FI

Food>, RH.. -J M~, GA., 19S3, H....... ..k-.. ....... 19SOo 

U.S. G


For oIow-....... pohoohoe. ....n__ ~Ies (1.5.... 

ohealhm.-... 3-10 m 1000: code I ia table 57.1) ....."..lormI becaose 

of thar....1bmaaI.....T_ 

wioh ouc1l ohmDoc....... 

........... 5-10 "C of...,Dbrioa wilh ia 1-2 .d 

"""llid n:.cHNJQUES 

0--. .d~ ............ shioIded !rom ia...... 

........ beat of by of • .....--ciaI beat (r.. 

57.68) or of aIumiauoo __it wilh. "-lIe to..oM! 

adact wioh metoI. A1tbooooh both sIUddiao tedDques ....... 0- 

.....J .........-..Iy.....~ __ "..lormI becaose of ina....d body 

........00. 1DOl>Wty. ud superim- vdibility aod ........ afforded .... 

ob.ervtn. At an opal b.v. channel or aa £root. the beet: tuit was frequently 

.... ooIy .dequole """""",,,,. 

T......... ia pohoohoe"'" ia _ ........... Aft« 

............... .....u-- ....m tip 10 7110-900 "C r... ....... 

secoDds. it was a.rted .Jowly to • depth ol10-2O em in aD area cl melt 

where ... crust had r...med. UudesinbIc orvwth oi..... icide or sbeotIo, 

partiaOrl, • problem wioh ....~~. could be .... 

mW:d by -u.. .... tip back .d Iortb slow iasatioo. 

Gmcrally, two people WO

S7. AA FLOW DYNAMICS. MAUNA LOA 1984 1567 

temperahU"e stablility, condition of the probe or path of sight, and quality of 

the geologic location. Confidence in the G-coded measurements grew as 

identical temperatures witJm ± 3 OC were obtained at the same locations 

day af.... day. both .. the ,."b and dawn the main channel. 

C-coded thennocouple measurements were made ~th6 in dow-moving 

pahoehoe that was insulated from the atmosphere or in aa where the probe 

tip penetrated into the 8utd core and remained stable for 5-20 minutes. 

Ideal. situations were pahoehoe toes fed by lava tubes that tunneled directly 

through the spalkr rampart. 11k! best situations for determining downflow 

lava temperatures were active pahoehoe fronts or margins. oozes through 

cracks in accretionary levees at the edges of the main channel. lava tubes fed 

by and near the channel, thick aa overflows near the chanod. and the 8uid 

cores of aa fronts. 

SAMPUNC AND OEN.5I1Y DETERMINATIONS 

Several types of samples were collected to study changes in chemistry. 

mineralogy, lex-tlU, and density of lite melt during the eruption. Many 

samples were colected concurrently with temperature measurements. Samples 

from the channels, channel overSaws. and pahoehoe were collected on a 

hammer or scoop, and were mediately quenched in water to stop growth 

of gas bubbles and devitriftcation. Spatter samples were watched in flight, 

picked up upm landing, and water quenched. Samples labeled "core" (fag. 

57.21, 57.22) were from intmors of aa flows. Some were collected from 

thermocoupk tips or hammers and quenched, but a few were collected after 

they had cooled ......aJJy. 

To obtain densities, the samples were diced to cubic or near-

USGS Professional Paper 1350, vol. 2 of 2

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