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Kellum, L. B., Devless, S. N., and Swimey, C. M., tion of F a g Mountah, a precaldera dacite dome
1945, Geology and oil possibilities of the south- adjacent to the 1912 vent, took place on the first day,
western part of the Wide Bay anticline, Alaska: because the inboard brow of its caldera-rirn scarp
U.S. Geological Survey open-file report, 17 p. lacks layer A and is mantled only by layer B and Later
Martin, G. C., 1926, The Mesozoic stratigraphy of tephra units. These units filled and obscured the cal-
Nsska: U.S. Geological Survey Bulletin 776, 493 de?, but concentric and radial fissures outline a 6-
PI krn depression. Subsequent growth of the Novarupta
Mutti, Emiliano, and Ricci Lucci, Frmco, 1972, Le lava dome end its ejecta ring was complete when the
torbidite delllAppennino setentrionale VTTS was discovered in 1916 (Griggs, 1922).
introduzione all'analisi de fecies: Societa At Mount Katmef, 10 km east of Novarupta,
Geologica ltaliana Memoir, v. 11, p. 161-199 second caldera (about 600 rn deep and also about 6 km 9
translated by Tor H. Nilsen, 1978, Turbidites of in area) is thought to have collapsed during these
the northern Apennines: Int~duction to facie events, apparently owing to some sort of hydraulic
analysis: American Geologiccil institute Reprint connection with the venting magmatic system. ?he
Series 3 (reprinted from international Geology floor of Katrnai caldera is similar in elevation to the
Review, v. 20, no. 2, p. 125-1661 preemptive 1912 vent. Observations by Griggs (1922)
Smith, W. R., 1926, G@olo# and oil developments of and Penner (1923, 1930) on the behavior of beheaded
the Cold I3ey district, Alaska, ~IJ Mineral glaciers, intracaldera fumaroles, and the cddera-Iake
resources of Alaska: Report on progress of level during 1916-23 support the inferred 1912 age of
investigations in 1924: U.S. Geological Survey Katmai cddera. All known ejecta, however, appear to
Bulletin 783, p. 63-88. have vented at Novarupta. A 20-m-thick pumiceous
debris-£low deposit at the southwest base of Mount
Katmai (Penner, 1950, pl. 1; Curtis, 1968, p. 201)
resembles an ash-flow tuff but consists of tephra that
remobilized down a single steep canyon-as shown by
We 1312 enpticm in the Vdey of Ten Tbwad uncharred wood, the absence of degasing features,
Smokes, Ketmai Nstid Park: A summary of the and a ratio of pumice-clast types unlike that of any
stratigraphy and peblngy of the ejecta 1912 ash flow but identical to that of the bulk pumice
faU on Mount Kiltmai. An andesitic tuff just inside the
By W a €Uldreal, Wth k Remtain, Anb ~nlt.ec', northrat rim of Katrnai caldera (Curtis, 1968, p. 204)
and Zarrg Jew
is a poorly sorted fall unit of pre-1912 age, zoned from
nonwelded material to a dense agglutinate. The
OW reexamlnatim of the 20th cenfury% m ~ 'rhorgeshoe t islandrt on the Katrnai caldera floor (Ctiggs,
vohrninous eruption, the 1912 outbmt in the Valley of 1922; Fmer, 1930, 1950) WE a severely eroded pla~ Ten mwsand Smokes (vm), wM initiated
dacite lava that plots off the 1912 compositional
to provide modern pet~chemica dab an a strongly trends (fig- 22) and may or may not have been erupted
zoned ealctc magmatic system; the splendld e-ures in 1912soon
stimulated e complementary study 02 the em- MLngling of three distincdwe magmas, both as
placement and welding of the tuf$ (area 2, fig. 19). Uqldds and as chilled ejecta, took place during the
The approximately 15 km erupted eruption, although there is no approach to homogcmIzaf
~ the m Novarupts cadera @t the head pf the VTTS lion between sharply defhed btind5 in the mixed
June &8, 1912, genelted abut 20 km of airfall eject&. Pumice in the idtid phian fd is 100 percent
teph end 11 to 15 km of =h-now tuff 60 rhyolite, but the later fall units (C-13) atop the ashhours.
Three discrete periods of dsh f a recorded at "ow sheet are more than 98 percent light-grey
correlate phian tephrtl layers in the dacite. Black andesitic scoria is Common only late in
V~TS that were respectively desimated A, DD, and the ash-flow sequence and in thin near-vent deposits
E-G by Curtis (1968). As much as 80 percent of the
Interbedded with the dac'te tephra layers,
ash-flow volume was tmptaced a single flow unit,
whi'h divided into graaW subunlt~ only dbully, where iTbT g:r ~ ~ h w ~ ~ r f r~ u y$ ~ o ~ ~ ~
velwity padients that developed in the halting flow
pro~ionr are 40 ;50:10. hnded
promoted internal shear and segregation. This main percent of all ejecta, consists of every combination
now unit is widely bg two to follr
but is predominantly rhyolite-andesite. Pumice counts
units af restricted areal extent, arid these units are, in at more than 150 localties show the first half of the
turn, capped by the stratified ak fd, layers c through ash-flow sequence to be 91 to 98 percent rhyolite;
H.
~uccessive pulses were alternately enriched in either
xquenoe ash overlqm with but daCite or andesite, es rhyolite decllned to less than 2
outlasted pumice fall A, and terminated about percent. The rhyofite-oop ash flows late in the
~ a
20 hoUW bf the initial 6utbreak and befo~ pumice fall
C. Layer B is a composite veneer that is latepally
to the sows, and layers E and H consist
mostly ,,itric dust settled dcrrin$. lulls after
each of the three pIinian eruptive inter"&. 'mca-
Sequence were less n~obfie and were progressively
channeled by ongoing compactio~ Novarupta dome,
the final unit emplaced, consists of highsilica rhyolite
contaminated by 1 to 2 percent of lithic debris and
dacitic PhenocrYsts end by about 5 percent of we&
defined bands of dacite.
After traveling about 16 km from the vent, the
'~epartrnent of Geology, Stmfd University,
Stanf d, CA 94305.
'Mill Valley, CA 91911.
rnaln ash flow was too deflated and sluggish to surmount
a 20-m-high moraine perpendicular to its path.
Pmts of the flow penetrated gaps in the moraine, and
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