Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

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Many of the feature names used in this report and on the included maps were assigned by the authors. These names are not officially recognized or approved by the U.S. Board on Geographic Names and are thus considered informal.
Selected Caves and Lava-Tube Systems In and Near Lava Beds National Monument, California By Aaron C. Waters, julie M. Donnelly-Nolan, and Bruce W. Rogers Introduction Lava Beds National Monument (fig. 1) lies on the north slope of the huge Medicine Lake shield (fig. 2), a complex volcanic edifice of greater volume than the steep-sided Mount Shasta volcanic cone, which towers as a snowclad land mark 40 mi southwest of the monument (fig. 3). Much of the north and south flanks of the Medicine Lake shield were built from molten lava transmitted through lava tubes. These tubes formed beneath the congealing surface of basalt flows in somewhat the same way that a brook may continue to flow beneath a cover of its own winter ice. As molten lava emerges from a vent and flows downslope, congealing lava from the top and sides of the central channel often forms a bridge over the lava stream. The sticking together of bits of lava spatter and fragile lava crusts strengthens the bridge in the manner that thin crusts of floating ice raft together to cover a brook during early stages of a winter freeze. Eruption of basalt lava, however, is a much more violent and spasmodic process than the steady gathering of water that feeds a brook. If liquid lava stops rising from its source deep within the earth, the still-molten lava moving beneath the crusted-over top of a lava flow will continue to drain downhill and may ultimately leave an open lavatube cave-often large enough for people to walk through. It is rare, however, to find such a simple scenario recorded intact among the hundreds of lava-tube caves in the monument. Even before the top and walls of a lava flow have time to cool during a pause in lava supply, a new and violent eruption of lava may refill the open tube, overflow its upper end, and spread a new lava flow beside or on top of the first flow. Even if the original tube is large enough to contain the renewed supply of lava, this tube must deliver the new lava beyond the end of its original flow and thus the lava field extends farther and farther downslope. If the gradient of flow flattens, the tube may subdivide into a number of smaller distributaries, which spread laterally over the more gently sloping ground. Within Lava Beds National Monument, most lava tubes are found within the basalt of Mammoth Crater (figs. 1 and 4). Complicated and intertwining lava-tube systems originating from Mammoth Crater and other vents have built a broad fan of complexly interfingering lava flows that form the northeast perimeter of the Medicine Lake shield. Most of this lava was delivered through lava tubes. Some tubes conveyed lava underground 15- 20 mi from their sources. Nevertheless, today one cannot walk for a distance of even 4 mi within any one lava tube. Large parts of the roofs of most lava tubes have fallen in, hiding the floor of the tube under huge piles of breakdown or angular broken rock, often stacked so tightly that access to both upstream and downstream portions of the tube is closed. In some places, however, collapse of the tube's roof has provided a large entrance into the lava tube through which one can walk with ease. In some collapse piles where access appears to be lacking, one can search the maze of tumbled blocks and perhaps find a crawlhole into a lava tube. Openings into caves may be detected by noticing the runways of small animals or testing the direction of air flow. On sparklingly clear, very cold winter days, openings into underground caverns will emit a white fog, just as one's exhaled breath does on such a day. Holes in the landscape surface formed by failure of part of a lava tube's roof are called collapse pits, breakdowns, or more commonly, collapse trenches (see maps 2, 5, 10, and 20; plates 1, 2, 4, and 6). While walking across the relatively flat surface of the lava flows, you are seldom aware of their presence until a large and deep hole yawns at your feet. Some small breakdowns are dangerous death traps for animals. Unwary humans have met a similar fate (see map 12, pl. 4, and the "Skull Cave" section). Once underground within a lava tube you may find your way impeded or blocked by a variety of features. Piles of loose rock that have peeled off the ceiling and walls of the tube may clutter the floor of the cave and slow your pace. Where no fallen blocks are present, the smooth to ropy (pahoehoe) surface of the lava on which you walk may change gradually to a very rough surface composed of bubble-filled loose blocks of a spiny (aa) lava. In some cases it may even completely block the cave entrance. The words pahoehoe and aa come from the Hawaiian language. Most lava tubes are found in pahoehoe lava (e.g. Greeley, 1971a; Harter, 1971), but occasionally they occur in aa lava (Guest and others, 1980). Geologists recognize several varieties of pahoehoe (MacDonald, 1953; Wentworth and MacDonald, 1953). The smooth but thin and partly congealed skin on the surface of the molten lava may become wrinkled and twisted into Introduction
Page 2 and 3: Lava cascade in Thunderbolt Distrib
Page 4 and 5: Frontispiece. Two visitors explore
Page 6 and 7: DEPARTMENT OF THE INTERIOR MANUEL L
Page 8 and 9: Caves easily accessible from Cave L
Page 10 and 11: PLATES [In pocket] 1. Caves of the
Page 14 and 15: Tulelake LOWER KLAMATH LAKE Prisone
Page 16 and 17: EXPLANATION ................... Lav
Page 18 and 19: flow, then the lava may pool behind
Page 20 and 21: "pull outs" where the dripping plas
Page 22 and 23: Mushpot, Catacombs, Ovis, and Merri
Page 24 and 25: Waters agreed to do the cave mappin
Page 26 and 27: into the distributary in the genera
Page 28 and 29: crawled 180 ft from the Mushpot tub
Page 30 and 31: es of plaster clog its continuation
Page 32 and 33: level of the tube. The southern ent
Page 34 and 35: surface collapse and only one comer
Page 36 and 37: dead-end passages on different vert
Page 38 and 39: and a roof covered with lavacicles
Page 40 and 41: puzzles abound in the Catacombs; do
Page 42 and 43: Ovis Cave Apparently, E.L. Hopkins
Page 44 and 45: thus forms a bridge over the broken
Page 46 and 47: pit is located along the southwest
Page 48 and 49: lava tubes, and the upper parts of
Page 50 and 51: occupies the lava pool just upstrea
Page 52 and 53: underway. Collapse to the surface h
Page 54 and 55: one located just below ceiling heig
Page 56 and 57: high, but it immediately widens to
Page 58 and 59: low depths along fissures. Many sma
Page 60 and 61: collapse (map 9, pl. 3). Two others
Page 62 and 63:
For a short distance below the coll
Page 64 and 65:
circle the two large downstream pil
Page 66 and 67:
where it opens into the north end o
Page 68 and 69:
water well, the cave changes marked
Page 70 and 71:
the older Schonchin Butte lava flow
Page 72 and 73:
here to the entrance, the tube is f
Page 74 and 75:
One cannot walk beneath it, as unde
Page 76 and 77:
Room-is actually a natural bridge,
Page 78 and 79:
pooled in the mouth ofthe tributary
Page 80 and 81:
perfection and cleanliness of its l
Page 82 and 83:
etween the benches. The levees are
Page 84 and 85:
tubes created a cave floor that is
Page 86 and 87:
cessive accretionary linings of lav
Page 88 and 89:
two levels were joined by a breakdo
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ft and passes through several level
Page 92 and 93:
stream, the ceiling heights drop, t
Page 94 and 95:
Cave. Collapse rubble half fills Cr
Page 96 and 97:
heights are between 12 and 20 ft in
Page 98 and 99:
Blue Glacier Room, where continuati
Page 100 and 101:
upstream from the one noted by the
Page 102 and 103:
Red Ice Room (fig. 63), which lies
Page 104 and 105:
tation that this tube system was fe
Page 106 and 107:
sured ground now occupies nearly tw
Page 108 and 109:
The larger and more interesting cav
Page 110 and 111:
part talus was reversed. Moreover,
Page 112 and 113:
long and 300ft in maximum width. Th
Page 114:
and lunar implications: Communicati
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Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

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