Geological Survey Bulletin 1673 Selected Caves and Lava Tube Systems in and near Lava Beds National Monument, California

In addition to the caves, shown on maps 1-7 of plates 1 and 2, that are easily accessible from Cave Loop Road, a number of interesting caves are easily reached by roads in other parts of the monument; these caves are shown on maps 8-14 of plates 3-5. Four additional caves that are among the most interesting in the monument are shown on maps 15-18 of plates 5 and 6; access to two of these caves, Crystal and Fern Caves, is restricted because of the fragility of their contents.

Two maps on plate 6 show surface features; map 19 shows Mammoth Crater and adjoining areas, and map 20 shows the short caves and interesting features associated with collapse trenches along a major lava-tube system within a little-visited part of the monument area.

Valentine Cave

Records at Lava Beds National Monument report that Valentine Cave (map 8, pl. 3) was "discovered and named by Ross R. Musselman on Valentine's Day, 1933." This cave can be reached from monument headquarters by driving southeast for 2 mi on the paved road connecting the monument to California Highway 139. As this road rounds the north end of Caldwell Butte, a paved road to the left (north) marked with a sign for Valentine Cave turns off and ends within 0.25 mi of the parking lot adjacent to the cave entrance (fig. 34).

Figure 34. Stairway leading to entrance of Valentine Cave (see fig. 4 and map 8, pl. 3).

Valentine is a deservedly popular cave among visitors—it is interesting, clean, and varied. Here one can see a lava-tube system that is only slightly damaged by collapse (see frontispiece). The cave shows most of the features to be found in lava tubes: pahoehoe floors, lava pools, lava cascades (fig. 35), and well-developed lavacicle ceilings and dripstone walls. Two kinds of lava benches are present: one marks a high-level stand of an extremely viscous lava flow, which attempted to crust outward from the walls as the lava was flowing; the second kind was made by the penetration and bulldozing of collapse blocks, due to hydraulic pressure from lava forcing its way through the tube. Large pillars around which the lava stream divided and reunited are present in the upper part of the cave. The central part of the cave contains lava falls and cascades through which the lava stream transferred from a higher lava tube to an open tube at a lower level. Downstream from this area of subsurface breakdowns Valentine Cave divides into distributaries, which are filled with lava downstream.

Figure 35. Lava benches on walls of Valentine Cave (see fig. 4 and map 8, pl. 3) indicate high-lava mark from higher stands of lava that occupied the tube.

The accessible passages within the cave total 1,635 ft. Most of the accessible area is in one main tube, blocked 950 ft downstream from the entrance by lava. The Valentine Cave entrance is a shallow collapse pit with an overhang upstream as well as downstream, but upstream access is blocked within 20 ft by roof collapse.

Surface Features Near Entrance

The size of the tube and its relation to surface features indicate that Valentine Cave continued much farther upstream and downstream. It can be traced upstream on the surface from a chain of collapse trenches, natural bridges, and short cave segments, which wind around the northwest side of Caldwell Butte. The basalt of Valentine Cave (Donnelly-Nolan and Champion, 1987) erupted from a set of spatter vents outside the monument, 1 mi southeast of Mammoth Crater, known as the Tickner Chimneys (map 9, pl. 3) and from additional spatter vents farther south. Tickner and Berthas Cupboard Caves (map 9, pl. 3) are in this same basalt flow just downstream from the vents and about 3 mi upstream from Valentine Cave. The basalt flowed north against the earlier basalt of Mammoth Crater, and then it flowed east and surrounded Caldwell Butte, and then it spread out north and east. Valentine Cave is within the north-trending lobe. There is surface evidence that a tube collapse 150 ft south of the entrance to Valentine Cave may have diverted the lava entering Valentine Cave at that time to the east; this diversion would have cut off the lava supply and allowed the now accessible portions of Valentine Cave to drain almost completely. The surface breakdown on the site of this collapse is rimmed by a rampart 10-20 ft high on its north side. This rampart was formed by lava forcing its way northward within a blocked tube. The ponded lava escaped through a tube that drained southeast from this point. The collapse rubble that blocks the head of Valentine Cave, only 100 ft north from this rampart, shows no sign of having been overrun by lava, although small slopover spills escaped northward between the upraised blocks of the rampart at a level 15 ft higher than the floor of Valentine Cave.

Schollendomes

The shallow collapse pit that gives access to Valentine tube is in a surface flow containing scattered schollendomes. Schollendomes are oval-shaped hills of lava, with a deep cleft running along the length of the hilltop. They form on some flows whose molten interior is still creeping forward after the flow surface has solidified. See Waters (1981) and figure 36 for descriptions of schollendomes in Captain Jacks Stronghold (fig. 4) at the north edge of the monument. Nichols (1946) shows photographs of similar features on the McCartys basalt flow in New Mexico, which he describes as pressure ridges. Wentworth and MacDonald (1953, p. 45) call similar Hawaiian features tumuli, which they state are "also known as pressure domes or schollendomes." They consider tumuli to be gradational into the more elongate forms known as pressure ridges. A detailed discussion of terminology and mode of origin is available in Champion and Greeley (1977).

Figure 36. Pathway through Captain lacks Stronghold (see fig. 4) follows axial trace of schollendome, which formed by cracking of chilled lava surface over molten interior. These natural trenches were utilized as defensive positions by the Modoc Indians during the Modoc War of 1872-73.

Upper Part of Valentine Cave

The first 350 ft of Valentine Cave downstream from the entrance contains many interesting features. At the entrance the tube is 25 ft wide and 8-10 ft high, but it immediately widens to 40 ft as it divides around a pillar 60 ft long and 20 ft wide. A second pillar of about the same dimensions is present 120 ft farther downstream.

The final surge of lava to pass through the tube was only 2-4 ft deep, and it left many records of its passage. Its surface began to crust over and solidify along the sluggish parts of the lava stream, such as the upstream and downstream ends of the pillars and in the alcoves along the outside walls. On the sides of the pillars and in other restricted areas of the tube, however, the sticky lava was pulled and sheared into ribbon-like masses, which piled up against one another in vertical sheets. In some places these accreted layers were later sheared off while other layers were added; thus, complex benches were completely torn off and carried away by the flood, and only a high-lava mark was left on the wall of the tube. In these highly sheared areas the wall below the high-lava mark is not covered with normal dripstone; instead it is smooth and shows only horizontal striations and grooves, where the viscous and partly solid lava was sheared and dragged along the wall.

In alcoves of the wall and on the upstream and downstream ends of the pillars these benches were able to grow out into the moving lava flood. Such areas are particularly significant because they record the fluctuations of the lava surface as well as indicating the velocity of the surges. No two areas are exactly alike. Moreover, between each accretionary layer, the dynamics of viscous flow are revealed not only by sheared surfaces but also by smeared-out bubbles, tensional cracks, and extended drag folds. A particularly good place to see some of these features is near the alcove on the east wall of the tube downstream from the second pillar (280 ft downstream from the entrance). Other excellent places are on the east wall between the pillars and on their upstream and downstream ends. These benches are labeled on map 8, plate 3.

The first 350 ft of Valentine Cave is a good example of a lava tube that has almost completely drained. The lava remaining on the floor is mostly pahoehoe; in places it is glassy and lustrous whereas at the cascades it is frothy. Only a small amount of soil and a few scattered collapse blocks litter the tube floor. Rodent pellets are present at several places and, where rainwater seeping through the roof has moistened them, their phosphatic composition causes a green fluorescent glow when a flashlight is played on them.

The ceiling of this part of the cave contains excellent lavacicles, and the walls above the benches display fine examples of lava dripstone. Many lavacicles are short thick blades resembling shark teeth. The roof of the cave is also riven with innumerable tight cracks, mostly tensional, formed as the lava cooled and solidified. They meet in triple junctions (three cracks radiating from a point). In addition there are a few long, straight cracks parallel to the course of the tube. Striking examples are present near the entrance west of the first pillar extending from it for over 100 ft. Percolating rainwater seeping through the roof along the cracks has loosened the lavacicle plaster from the wall rock above. A few large blocks of the roof have tumbled to the floor, and many others appear ready to fall.

Percolating water also produced an other interesting effect on the roof. Water wets the surface along both large and small cracks and drips to the floor from their edges. Most of the water evaporates and forms a thin precipitate of white caliche (calcium carbonate). Because of the strong color contrast between the white caliche and the shiny black lavacicles, the roof of many parts of Valentine Cave appears to be a mosaic of irregularly shaped black tiles held together by a white cement.

Two Central Breakdowns

An abrupt change in the Valentine Cave occurs 370 ft downstream from its entrance. The width of the tube, 30-50 ft in the upper part, closes to 12 ft, and the floor drops over two long cascades and three small lava falls into a broad compound lava pool at the bottom of the slope. The tube is over 75 ft wide in this pooled area.

Just above the head of the cascades three small tubes split off from the main tube. One enters the west wall a few feet upstream from the head of the cascades and is filled with frothy pahoehoe. The other two tubes, 4-7 ft wide and 3-5 ft high, take off from the east wall on a northeast course but then turn back to the north. Nearly 90 ft downstream they merge together around a kidney-shaped pillar 85 ft long and 20 ft thick. In the lower 25 ft of their course the lava in these high-gradient tubes cascaded down a steep slope, which drained their combined flow into the southeastern part of a large compound lava pool. This pool also received the flow from the main tube's cascades 40 ft farther west.

The upstream parts of these two tubes are good examples of lava tubes that have been completely drained. They have typically flattened oval cross sections with a broadly rounded roof and floor that curves sharply upward at their walls. These tubes also contain excellent examples of dripstone walls and lavacicles. At their lower end, where the steep cascades begin, their floors drop abruptly 8 ft to a lava pool. The final trickle of lava into this pool arrived in a narrow channel cut a foot deep into the floor of the lava cascades. The roof of the tubes, however, does not drop with these cascades but instead arches northward over them to extend high over the eastern part of the wide pool area.

On the east side directly downstream from the easternmost of the two small tubes is a sloping lava bench located 3-8 ft above pool level. Its upper surface is covered with pahoehoe whose ropes clearly show that lava from the eastern small tube once flowed over this bench. The latest channel of the eastern tube turned sharply to the left and cut through this bench. Its truncated edges are evidence that the bench originally was a large pile of tumbled roof blocks, which were later completely immersed in molten lava. This lava carried away parts of the collapse and the bench was left as a remnant. The channel forms a steep cascade that joins the cascade from the other small tube. A similar bench, in which fallen collapse blocks coated with lava are clearly visible, is present in the alcove on the same wall 20 ft farther downstream.

The compound pooled area, which was fed by the main tube and these two small tubes, is in a room roughly divided into northwestern and southeastern parts by two small pillars. Both pools have floors at approximately the same level, and the lava from both flowed downstream through a tube only 18 ft across—a width contrasting strikingly with the 75-ft width of the pooled area.

The roofs of the two parts of the pooled area, however, are very different. The roof of the lava pool northwest of the two pillars is a broad expanse of lavacicles, which lie only 2-4 ft above the pool's floor. In contrast, the roof on the southeast side of the pillars is 10-20 ft above the pooled surface and is dominated by a variety of collapse features. The former course of two small lava tubes, whose floors collapsed into this huge room, can be followed for tens of feet by their outlines indented in the roof of the large room. It is evident that several tubes on different levels merged to form this room and that the collapses which joined them together occurred prior or even during the last time that Valentine Cave was filled with molten lava. Much of the collapse debris was carried away in the molten floods, but some was left as benches and as alcove fillings of collapsed blocks penetrated and smoothed over by the flowing lava. More debris probably lies completely buried by congealed lava at the bottom of the two lava pools.

The last lava to course through Valentine Cave flowed out of this pooled area in a broad pahoehoe stream, which pooled again after flowing only another 40 ft. This pool is the floor of another complicated area of tube junctions and roof collapses forming an irregular Y-shaped room 600 ft downstream from the cave entrance. At this point Valentine Cave divides into two major distributaries—one continuing to the north and the other (and larger) tube trending N. 70° E.

The most striking feature in this second large room is the pile of roof collapse debris that partially blocks the north-trending tributary and spilled collapse blocks halfway across the Y-shaped lava pool. The collapse pile, although it rises high into the roof, does not provide access to the surface. The distributary tube to the north can be easily entered by skirting the collapse pile along the west wall of the tube.

Downstream Distributaries

The Millipede Distributary extends north 180 ft then turns 45° to the west (map 8, pl. 3). It narrows abruptly to a short crawlspace, then expands into a pahoehoe pool roughly 25 ft in diameter, but the roof is less than 3 ft above the pool's surface. This pool ends the accessible part of the north branch of Valentine Cave. The tube contains excellent lavacicles, dripstone walls, and pahoehoe floor. There are two small areas of roof collapse 60 and 80 ft from its downstream end and a huge roof collapse at its junction with the main tube.

The northeast-trending Bubble Distributary is more diversified. Within the second area of breakdown about 180 ft downstream from where this tube begins are benches on either side; both benches consist of collapse breccia partly eroded by flowing lava. Evidently the collapse that partly blocks the tube junction was preceded by one or more collapses, which spilled blocks into the molten lava. One large pile of collapse blocks that was cemented by lava fills a large alcove on the north wall of the distributary at its source. As the lava level lowered within the tube, this collapse pile first appeared as an island above the flood. With further drainage, a trough appeared between this "island" and the wall of the tube. High-lava marks indicate backflow in the upstream direction within this trough (see map 8, pl. 3). Several alcoves farther downstream contain piles of collapse breccia that were bulldozed into these sheltered spots by the moving lava. During the last stages of drainage many of these piles were connected by a discontinuous lava bench, which bordered both sides of the tube and widened across the alcoves. Between the benches is an open channel, which is 2-3 ft deep. The final surge of lava down this part of the tube built a lobe of spiny pahoehoe, a little thicker in its center than the channel is deep. In most places, however, it did not completely fill the channel but left a small gutter between the wall of the channel and the rounded surface of the frothy pahoehoe lobe. In a few places this last lobe of lava developed a spiny surface and began to break up into separate blocks, and so the lobe is transitional toward aa. Many peeled linings are present along this section of the passage.

Parts of this tube have low ceilings, and it is evident that the tube is filled with congealed lava downstream. Finally the tube again splits into north and east distributaries. At this split the benches disappear and smooth pahoehoe that formed pools as it rose left only a crawlspace between the ceiling and floor. This north distributary is filled and becomes inaccessible only 15 ft from the junction. One can crawl down the east branch for 75 ft to a lava boil on the floor. This lava boil may represent an overflow from a lower tube possibly fed from the twin lava pools several hundred feet upstream. Just past this boil the passage is sealed by a lava pool.