Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

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long and 300ft in maximum width. The rim of the breakdown is continuously surrounded by a rampart of talus and tilted roof blocks ranging in height from 8 to 20 ft. However, before the rampart was formed, the heart -shaped area had sagged in toward the center of the depression, and so the rampart itself is surrounded by a "moat" up to 8ft deep. Most interior breakdown now consists of a "cork" of somewhat broken and variously tilted, but still relatively intact, roof rock. The inner edge of the breakdown is separated from this central cork by talus and broken rock, which spread from the low cliff of the breakdown and from the shattered edges of the cork (map 20, pl. 6). The position of the large lava tube apparently was beneath the west side of the heart-shaped depression. The blocked cave upstream projects into the west side of the depression, whereas at the widest part of the depression a skylight drops into another segment of tube. Also near this part of the depression a shallow collapse trench of the normal width for the tube leaves the breakdown and continues to the east side of the next large breakdown to the north. This collapse trench extends north-northwest for 440 ft, changes into a 250-ft-long shallow linear sag with narrow turndown sides, and disappears 70 ft short of the southeast comer of the next breakdown The next breakdown is shaped like a rectangle with rounded-off comers. It is similar in size but a little smaller than its heart-shaped companion. A mixed block-and-tilted rampart 8-35 ft high surrounds the collapse with part of this rampart standing in a moat 2-8 ft deep. The interior of this breakdown, however, does not contain any intact cork. Instead a hummocky carpet of loose blocks spreads from all sides. The four breakdowns that complete the N. 40° W. trend are fairly shallow collapse trenches of a size and depth consistent with the collapse of a tube averaging 30-50 ft wide. They are distributed in two pairs of small breakdowns with 345 ft of relatively uncollapsed lava tube between. A skylight 45 ft deep punctures the west edge of a lava-tube cave at a point 50 ft north of the southern pair. A small fissure that deviates to the northeast from the south side of the northern pair has a small block rampart rising above it. At the downstream end of the northem pair the lava-tube system turns on a N. 10° E. course and maintains this trend for a distance of a little more than 1 mi. It then fades out into a widespread area of low sag basins north of the Three Bridges area. The actual walking distance is more than a mile because this part of the lava-tube system meanders in a series of broad open curves. Many interesting features occur along this stretch of trench, and most are variations of features previously described. The first breakdown is rimmed by a block rampart 8-20ft high, parts of which are bordered by a moat as much as 5 ft deep. A skylight is present at the northwest comer of the collapse, whereas on the opposite (east) side a schollendome with almost vertical sides may indicate a second lava tube that contributed to the collapse. Both of these inferred lava-tube caves appear to converge farther north into a curving (concave to the west) small breakdown. At the north end of this breakdown a cave can be entered that swings to the east, almost at a right angle to the former trench. At the northeast end of this cave, a very large oval breakdown 980 ft long and 350ft wide trends N. 10° E. Block ramparts 15-20 ft high are perched above its north periphery, but they lower to 10-12 ft around its south end. The interior of this large collapse consists mostly of hummocky piles of loose blocks, but a dozen large fragments of the roof can be shown on the map. The largest is a thin flat-topped table 430 ft long (labeled on map 20, pl. 6 as "table") that occupies the north-central part of the breakdown. A smaller oval breakdown overlaps the northwest comer of the large collapse. It has no ramparts, and its central part is a cork of intact roof rock, warped into a spoon shape at its northwest end. A cave curves sharply right from the north end of this breakdown and then 200 ft farther downstream turns sharply left and connects with a collapse pit about 50 ft in diameter. This lava tube is the first of the three caves separated by breakdowns that inspired the name "Three Bridges." The smaller breakdown between the first and second caves is separated by a sill from a larger 320-ft-long and 75- ft-wide larger neighbor. A spillover channel lies over the sill. This breakdown is rimmed on all sides by a hydraulic rampart ranging from 5 to 15 ft high and sits in a narrow moat as much as 5 ft deep. At the downstream end of this breakdown a small collapse pit provides entrance into the second section of lava tube-a cave 260ft long-which, in tum, is interrupted at its north end by a section of collapse trench 330 ft long. At the downstream end of this trench the third cave extends 220 ft to where it is interrupted by a collapse pit. Another cave entrance is present on the north side of the collapse pit, but we did not explore this cave beyond its entrance. North of the Three Bridges is a broad area of indefinite shallow sag basins and a few linear streaks that may be surface lava channels. The course of the lavatube system across this area is indefinite, probably because the main tube split into a cluster of anastomosing smaller tubes. If so , some of these reunite downstream and continue the overall N. 10° E. trend beyond the north edge of the map area. The offset in the lava-tube system just north of the Three Bridges area (map 20, pl. 6) was inferred primarily from anastomosing tube channels associated with the shallow sag basins. Two additional tiny breakdowns lie directly on this line within the belt of indefinite sag basins. Other, larger breakdowns are enclosed within still larger sag basins to the west. Farther northeast four other large collapses are clustered within one large sag basin with indefinite boundaries. Another large collapse lies still farther north inside a much larger shallow sag basin. As mentioned previously, the lavatube system continues northward beyond the map area, then it swings eastward toward Juniper Butte (fig. 4), and then it probably continues northward to Fern Cave. Along its easterly course it spawns many distributaries to the northwest and north. 100 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California
Schonchin Butte Flow As can be seen from map 20, plate 6, the east edge of the Schonchin Butte flow and this lava-tube system are roughly parallel. Although the margin of the Schonchin Butte flow (fig. 70) is deeply indented on a small scale, its east edge is seldom more than 0. 25 mi west of the trace of the lava-tube system from White Lace Cave to beyond the north edge of the map area. The Schonchin Butte flow is older than the basalt of Mammoth Crater whose mostly pahoehoe flows lap against the blocky east edge of the andesite of Schonchin Butte. Schonchin Butte (fig. 67) and its neighbors Hippo Butte, Crescent Butte, and Bearpaw Butte had been built to their present dimensions (and Crescent Butte had been deeply eroded) before the basalt flows from Mammoth Crater were erupted (figs. 1 and 4). These basalt flows, transmitted mainly through lava tubes, impinged against and ultimately surrounded the basal parts of the older buttes. The chains of breakdowns that now mark the lava-tube systems are situated at the crest of low ridges on this northward-sloping lava plain because levees, overspills, and distributaries constantly ·built the ground surface higher adjacent to the major lava-tube systems. The Schonchin Butte flow is a large multiple flow consisting of countless overlapping narrow and wide lobes of aa and block lava. The flow erupted out of a boca on the east side of Schonchin Butte (fig. 67), a conspicuous landmark in Lava Beds National Monument. The lava that formed the Schonchin Butte flow is of different composition and was considerably more viscous than the Mammoth Crater lava. Its surface features are almost entirely of aa and of block lava. Such lava is crowded with tiny bubbles and was already partly crystallized when extruded, so its partly congealed surfaces broke up into blocks as it slowly moved forward. These physical features explain why it piled up in steep overlapping lobes, each with a steep front and sides of talus. The fronts and sides of major lobes may be bordered by steep loose talus slopes or by treacherous cliffs of slightly agglutinated blocks. Such flow fronts may be from a few feet to more than 100 ft in height. From this brief description it is apparent that the Schonchin Butte flow, 4 mi long and 1.5 mi wide, is an obstacle to all traffic. Only the major flow lobes along this part of its periphery (map 20, pl. 6) are shown. An experienced outdoor person, equipped with excellent boots and heavy gloves, may require 2 or more hours to get across the flow. A FINAL NOTE A great deal can be learned about lava flows by studying lava-tube cave systems because they preserve the fascinating and precise records that reveal the mechanics of volcanic flow, which operated in former infernos. Moreover, you can examine these records and ponder them at your leisure in the cool, quiet environment of a cave without the apprehension involved in personally witnessing an active eruption during the creation of a lava tube. While watching actively flowing lava, you can only guess at what goes on beneath the flow surface while your mind is intermittently occupied by the overriding question, "Am I at a safe distance?" You do not need to be a scientist to enjoy the caves or even to write articles about them. If you are interested in some special feature, such as lavacicles or tube-in-tubes, safe and enjoyable cave trips can be planned using the text and maps of this report. Then study the appropriate maps and descriptions, and always take the map with you when entering the cave. Remember that multiple lights are necessary for all caves except Mushpot, and that access to some caves may be restricted. Information about access is available at the Visitor Center, where important exploration and safety guidelines are also distributed. REFERENCES CITED Anderson, C.A., 1941, Volcanoes of the Medicine Lake highland, California: University of California Publications, Bulletin of the Department of Geological Sciences, v. 25, no. 7, p. 347--422. Brown, Dee, 1970, The Ordeal of Captain Jack, Chapter 10 in Bury My Heart at Wounded Knee; New York, Holt, Rinehart, and Winston, p. 219-240. Champion, D.E., and Greeley, Ronald, 1977, Geology of the Wapi lava field, Snake River Plain, Idaho: p. 133-151 in Greeley, Ronald, and King, J.S., Volcanism ofthe Eastern Snake River Plain, Idaho: A comparative planetary geology guidebook: National Aeronautics and Space Administration, Washington, D.C. Donnelly-Nolan, J .M., 1987, Medicine Lake volcano and Lava Beds National Monument, California: Geological Society of America Centennial Field Guide Cordilleran Section, p. 289-294. Donnelly-Nolan, J.M., 1988, A magmatic model of Medicine Lake volcano, California: Journal of Geophysical Research, v. 93, p. 4412--4420. Donnelly-Nolan, J.M., and Champion, D .E., 1987, Geologic map of Lava Beds National Monument, northern California: U.S. Geological Survey Map 1-1804, 1:24,000 scale. Greeley, Ronald, 1971 a, Geology of selected lava tubes in the Bend area, Oregon: Oregon Department of Geology and Mineral Industries Bulletin 71, 47 p. Greeley, Ronald, 1971b, Observations of actively forming lava tubes and associated structures, Hawaii: Modem Geology, v. 2, p.207-223. Greeley, Ronald, 1972, Additional observations of actively forming lava tubes and associated structures, Hawaii: Modem Geology, v. 3, p. 157-160. Greeley, Ronald, and Hyde, J.H., 1972, Lava tubes of the Cave Basalt, Mount St. Helens, Washington: Geological Society of America Bulletin, v. 83, p. 2397-2418. Grove, T.L., Gerlach, D.C., and Sando, T. W. , 1982, Origin of calc-alkaline series lavas at Medicine Lake volcano by fractionation, assimilation and mixing: Contributions to Mineralogy and Petrology, v. 80, p. 160-182. Guest, J .E., Underwood, J .R., and Greeley, R., 1980, Role of lava tubes in flows from the Observatory Vent, 1971 Eruption on Mount Etna: Geological Magazine, v. 117, p. 601-606. Harter, R. G., 1971, Bibliography on lava tube caves: Western Speleological Survey No. 44, Miscellaneous Series, Bulletin 14, Los Angeles, 52 p. Hatheway, A.W., and Herring, A.K., 1970, The Bandera lava tubes of New Mexico, References Cited 1 01
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Lava cascade in Thunderbolt Distrib
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Frontispiece. Two visitors explore
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DEPARTMENT OF THE INTERIOR MANUEL L
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Caves easily accessible from Cave L
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PLATES [In pocket] 1. Caves of the
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Many of the feature names used in t
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Tulelake LOWER KLAMATH LAKE Prisone
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EXPLANATION ................... Lav
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flow, then the lava may pool behind
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"pull outs" where the dripping plas
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Mushpot, Catacombs, Ovis, and Merri
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Waters agreed to do the cave mappin
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into the distributary in the genera
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crawled 180 ft from the Mushpot tub
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es of plaster clog its continuation
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level of the tube. The southern ent
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surface collapse and only one comer
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dead-end passages on different vert
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and a roof covered with lavacicles
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puzzles abound in the Catacombs; do
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Ovis Cave Apparently, E.L. Hopkins
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thus forms a bridge over the broken
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pit is located along the southwest
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lava tubes, and the upper parts of
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occupies the lava pool just upstrea
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underway. Collapse to the surface h
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one located just below ceiling heig
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high, but it immediately widens to
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low depths along fissures. Many sma
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collapse (map 9, pl. 3). Two others
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Page 82 and 83: etween the benches. The levees are
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Page 108 and 109: The larger and more interesting cav
Page 110 and 111: part talus was reversed. Moreover,
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Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

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