Lava cascade in Thunderbolt Distributary of Labyrinth Cave system

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thus forms a bridge over the broken-up floor jam of balcony blocks. Upstream 95 ft-just southwest of a collapse to the surface-the floor of the upper level has tumbled so completely that its former position is recognized only by a few small balcony remnants 4-6ft above the jam of collapsed balcony rubble that forms the present floor of the cave. The explanation for these relations is clear. These floor jams and balcony remnants show that the upper level, from the former skylight northeastward, is an unstable fill formed within the middle level. After its 90° bend, the middle level rejoins the small upper tube at the former skylight. What we see from the skylight northeastward is the record of a high-lava fill in the middle level, which persisted at this height long enough for its top to completely solidify from wall to wall. After a solid crust less than a few feet thick had formed, the molten lava beneath continued downstream and ultimately drained to a level 5 ft or more below its former stand. This allowed part of the crusted-over floor to subside and thereby form a jam of balcony blocks in parts of the tube and a bridge in a narrow part close to the roof. The balcony level also survived completely intact in the small upper tube, which continued straight. Remnants of thi s balcony, changing in places to sloping alcoves, also occur along the middle level all the way to its head in the shallow collapse basin. In summary, this shallow collapse basin and the middle level of Paradise Alleys constitute the main distributary that supplied lava to the Catacombs system of lava tubes. The lower and upper levels, the balcony, and the floor jams are interesting supplementary records of fluctuation in the height of the lava in both the Paradise Alleys and in the Catacombs Cave. Former Skylight The former skylight just east of the entrance to Paradise Alleys provides further evidence of a high-level stand of the molten lava pouring through the Paradise Alleys tubes. The lava overflowed and spilled out to the north and east onto the surface through the skylight. The more prominent spillovers are indicated by dashed lines (enclosing arrows that indicate the direction of flow) on map 4, plate 2. Spillovers from the last highstand of Catacombs Basin lava lake are similarly shown. Natural Bridge Area Large, spectacular collapse trenches are present in the area where Cave Loop Road crosses the Mammoth Crater-Post Office Cave line of breakdowns over the feature named the Natural Bridge (map 5, pl. 2). This bridge also marks the point where the feeder tubes from Mammoth Crater began to subdivide into the numerous distributaries that built the sloping plain and the numerous tubes of the Cave Loop Road area (fig. 14). The Paradise Alleys-Catacombs Cave system and the Hercules Leg-Juniper Cave system have their upstream beginnings here. Four short near-surface lava-tube caves-Sunshine, Battered Sherman, Juniper Pole, and Gail-are within this area, as are numerous small spillover lobes of lava, small collapse basins, and miniature breakdowns, and lava trenches. Because the deep collapse trenches are large features, the scale chosen for the Natural Bridge area map is reduced more than that of the other maps. To clarify the spatial relations between the trenches and nearby cave systems, the area around Ovis Cave, the head of Paradise Alleys, and the part of Hercules Leg Cave upstream from its entrance have been replotted on map 5, plate 2 at a larger scale. Short remnants of two large feeder tubes have survived nearly intact beneath Natural Bridge. One can walk through two strands of the upper tube (separated by a pillar) and visit a short section of the lower tube through crawlholes. The easiest and most interesting way to visit one of these large tubes, however, is to take the trail through Ovis Cave. Ovis Cave's position and the trails at its downstream end are shown on map 5, plate 2. Ovis Cave, the tube under Ovis Bridge, and the upper tube beneath Natural Bridge are all remnants of the same large lava tube. Battered Sherman Cave and Sunshine Arch are located along the lava channel leading to Sunshine Cave. Large Collapse Trenches The most spectacular features of the Natural Bridge area are the deep collapse trenches. However, the amount of space within the central part of such a trench, as between Natural and Ovis Bridges, presents an interesting puzzle. This trench definitely is too deep and voluminous to be ascribed to a roof fall in the upstream continuation of the lava tube in Ovis Cave. How then is the additional room in this trench to be explained? There are three possibilities. (1) The tube increased in size upstream, due both to a thinning of the roof and to a deepening of the channel, (2) two or three tubes were superposed one above the other, and all of them have collapsed together, or (3) collapse began while lava was actively flowing through the tube, and the fallen blocks were rafted down the tube before volcanism ceased. From evidence downstream (map 4, pl. 2, map 15, pl. 5, and map 18, pl. 6, and "Ovis," "Post Office," and "Crystal Cave" sections) it is apparent that multiple collapse is the most probable explanation. In fact, by superposing the map of Ovis Cave on that of Crystal Cave one notes that the deepest tube exposed in Crystal Cave lies demolished beneath the deepest section of the trench between Ovis Bridge and Ovis Cave. The second theory sufficiently explains the added space in the deep trench between Natural Bridge and Ovis Bridge. Consistent with this explanation, the profile of the talus on the walls of this trench shows a narrow medial trough with steep cliff sides giving way to gentle talus slopes higher on the walls-the profile to be expected because the lower tube in Crystal Cave is smaller than the one that formed Ovis Cave. The very large collapse trench that lies upstream from the Natural Bridge, however, contains evidence of a much more complex history that may involve all three processes. This trench shows 32 Selected Caves and Lava-Tube Systems, Lava Beds National Monument, California
clear evidence of having developed from an earlier collapse after which molten lava lay ponded in a wide lava lake or sluggish stream open to the sky during at least some major periods of volcanism. Today the rock rim of this trench is a cliff ranging from a few feet to 45 ft in height. From the base of the cliff a talus slope of loose blocks descends to the deep central part of the trench, which is at the projected elevation of the two large superposed lava tubes beneath Natural Bridge. The deepest hole within this collapse trench is at the trench's extreme northeast corner, directly beneath the upstream entrance to the caves beneath Natural Bridge. Here, a collapse that extends through the upper tube and into the lower tube beneath Natural Bridge has formed a pit over 50ft deep. This pit is bordered on the southwest by a steep ridge of tal us that forms a berm across the head of the trench and divides the main part of the trench from the deep hole just upstream from Natural Bridge. Only near this cave entrance can any clearcut relation be seen between the trench and the passages of the lava tubes. It is clear that both the upper and the lower lava tubes exposed beneath Natural Bridge extended upstream into the northwestern part of the area now occupied by the deep collapse trench. Yet a simple calculation will show that the volume of the collapse trench is at least three times greater than the space required to completely fill lava tubes the size of those beneath Natural Bridge, which are almost certainly the upstream continuations of Ovis Cave and the lower tube in Crystal Cave. No remnants of other tubes that might help with thi s space problem are known. If they ever did exist, which seems unlikely, they are hidden in the talus of the collapse trench. Other interpretations of the history of this trench can be inferred from a study of the rock rims along its borders. First we note that the highest elevations around the trench are on these rims; the sagebrush-covered ground on both sides slopes away from the trench, not toward it. As indicated on the map, molten lava spilled over the trench rim as small lobes in many places. Some lobes escaped over the rim through low areas along the northwest side and then coursed northward down the slope. A larger lobe, which contains Sunshine Cave, spread beyond the area of the map. The Sunshine Channel, at the head of this cave, and its connection with the trench, is shown on an inset of the Natural Bridge map (map 5, pl. 2); its passages are described in the section "Battered Sherman Cave and Sunshine Arch." The Sunshine Channel is partly lava gutter and partly small lava tube; farther downstream it is still roofed over to form Battered Sherman Cave; a miniature natural bridge, Sunshine Arch; and the upper part of Sunshine Cave. Note that where the channel leaves the big collapse trench, backflow features developed. Thus it was a lowering of the lava lake within the large collapse trench that stopped the filling of Sunshine tube and allowed it to drain and survive as an open cave. Lava-Tube Caves in the Natural Bridge Area Ovis Cave, Paradise Alleys, and Hercules Leg Cave all have their upstream entrances within the Natural Bridge area. Ovis Cave and Paradise Alleys are shown on map 4, plate 2, Hercules Leg and Juniper Caves are shown on map 6, plate 2. Caves shown on map 5 (pl. 2) of the Natural Bridge area include: (1) a complex of two large lava tubes and two small lava tubes beneath Natural Bridge; (2) Gail Cave, a small lava tube with two collapse basins strung along it, which can be traced for 400 ft northeast after branching from the upper tube beneath Natural Bridge; (3) Juniper Pole Cave, south of the embayment at the southeast comer of the large collapse trench upstream from Natural Bridge; (4) Sunshine Cave, Battered Sherman Cave, and Sunshine Arch, northwest of Natural Bridge; and (5) Duffys Old Still Well and Prohibition Cave, upstream from the segment of deep collapse trench. Caves Beneath Natural Bridge The caves beneath Natural Bridge are remnants of four different lava tubes, each of a different size and at a different elevation; all these caves can be entered from the large passage beneath Natural Bridge. At the downstream (northeast) side of Natural Bridge is a large arched cavern 12 ft high and 40 ft wide. It quickly narrows to half this width, because a slide of loose blocks spilled onto the floor from a collapse of part of the southeast roof and wall. Farther upstream 80 ft, however, the tube suddenly widens on both walls, subdivides around a 75-ft-long pillar, and then reunites at the pillar's upper end. In another 20 ft the single tube, now 20 ft high and 45 ft wide, was demolished by the northeast end of the deep collapse trench, which forms the southwest side of Natural Bridge. This tube, labeled "upper tube" on map 5, plate 2, is almost certainly the upstream continuation of the large tube that forms Ovis Cave. Another remnant of it forms the opening beneath Ovis Bridge. Beneath the upper tube is another large tube-the Hummingbird Flyway. It does not split around the pillar like the upper tube but continues upstream beneath the area adjacent to the pillar (see the cross section of Natural Bridge on map 5, pl. 2). Only about 60 ft of this lower tube is accessible; the rest of it (southeast of the pillar) was demolished by collapse of the upper tube's floor. Along part of this collapse, however, the southeast wall of the lower tube can be traced, curving up in places beneath an overhanging ledge formed by the broken floor of the upper tube. In this stretch the Flyway is more than half filled with collapse debris. Two crawlways and a pit permit entry into the relatively undamaged part of the lower Hummingbird Flyway tube. One crawlway is located in the upper tube 15 ft southwest from the downstream edge of Natural Bridge, at the northeast margin of the slide that spills out from the southeast wall. The second crawlway is through a maze of huge collapse blocks where the southeast wall of the upper tube swings out around the pillar. It is near the northeast corner of the collapse that dropped part of the floor of the upper tube into the lower tube. The Natural Bridge Area 33
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 12 and 13: Many of the feature names used in t
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 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
Page 90 and 91: 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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