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

Kirk Whites and Beaconlight Caves

Downstream from Merrill Ice Cave along the same tube system are Kirk Whites and Beaconlight Caves, two short but large caverns. They are remnants of a lava-tube system, which heads in the steep schollendome front of a lava field, which erupted from Mammoth Crater. The tube system begins where the lava flowed northward through the gap between Hippo and Bearpaw Buttes (fig. 4). The tube's former position can be traced by a line of collapse trenches, which starts at a horizontal hole in the schollendome front north-northeast of Modoc Crater and crosses the east side of Bearpaw Butte to Bearpaw Cave. Donnelly-Nolan and Champion (1987) believe instead that Modoc Crater was the point of origin of this major tube. Whether the lava came from Modoc or Mammoth Crater, it was all part of the same eruptive event. From Merrill Ice Cave the line of collapse trenches zigzags to the base of Schonchin Butte, where it skirts around the south and east sides of the older Schonchin Butte lava flow. Kirk Whites, Beaconlight, Skull, and Frozen River Caves are located along this tube system. The line of trenches (map 20, pl. 6) extends north for another 6 mi and then turns east. Many distributaries fan out toward former Tule Lake (fig. 1), although one major tube may continue east and then north to Fern Cave.

The large lava field built by flows from this major lava tube is older than the one built from the feeder tubes in the Cave Loop Road area. Roof collapse ruined far more of the underground passages along this lava tube than along the Cave Loop Road lava tubes. The large collapse trenches and pits that resulted are spectacular features of the landscape when viewed from an airplane, but on the ground most are invisible until you approach their rims.

Between the collapse trenches are natural bridges and short caves that reveal parts of the underground lava-tube system. Most such caves, however, are disappointing to the student of underground "lava plumbing" because they have been greatly defaced by the unraveling of rock from their walls and roof, a process that continues today. Overhead are many loosened blocks held precariously against the side of a neighboring loose block. Along the walls are slides of loose talus. The floors of such caves are difficult to traverse because blocks of all sizes clutter their floors and may shift under your weight when you step on them.

Kirk Whites and Beaconlight Caves are typical of the many short caves that lie along this line of collapse trenches. We chose to study them because they are near the paved road through the monument. Caves along this line between Merrill Ice Cave and Skull Cave include Castle, Kirk Whites, The Igloo, Beaconlight, Symbol Bridge, and Irish Bridge. Caves downstream from Skull are Ship Cavern, White Lace, Big Painted, Peninsula Bridge, Frozen River, and Captain Jacks Ice Cave. Most of these are shown on map 20, plate 6—a reconnaissance map of the collapse trenches from Skull Cave to the Three Bridges area.

Kirk Whites Cave

Kirk Whites Cave (map 11, pl. 4), named by J.D. Howard, has a large entrance room 185 ft long, 60-70 ft wide, and 20 ft high. Enter the cavern on the trail built in the 1930's by the Civilian Conservation Corps and note that the original roof and walls have been obliterated throughout the cave by slow unraveling from rockfalls. The floor, except for a small space at its upper end, is completely covered with thick piles of collapse debris including many very large blocks. Details of the massive lava flow in which the cave developed can be seen in places along the wall of the cavern, but they are better displayed on the northwest wall of the collapse trench.

Near its upstream end the cavern tapers to a width of 35 ft, and then nearly the full width of its floor falls away into a lower tube, the Mouseoleum. Remnants of the pahoehoe lava that formed the true floor of the original lava tube are left as overhanging ledges around parts of the rim of this collapse pit. Two small holes through the pahoehoe floor at the northwest corner of the entrance cavern provide a relatively easy entry into the lower tube; however, there is little to see. Upstream and downstream it is completely closed by collapse blocks that have fallen from the walls or been dumped through its roof, and only a small room 45 ft in diameter, which is one-half to two-thirds filled with collapse blocks, remains. In the few places where a true wall of the lower tube is exposed, dripstone forms a thin coating over red volcanic breccia instead of the basalt flow that enclosed the upper cavern. Underneath the overhanging ledges that partly ring the top of this room, the nearly horizontal contact between this red breccia and the overlying flow is visible in places. It was the collapse of this unstable red breccia inward through the walls of the lower tube that destroyed the tube's continuity upstream.

The Igloo

Of greater geologic interest, although smaller than Kirk Whites Cave, is The Igloo, which lies at the opposite (southeast) end of the collapse trench that also provides the entrance to Kirk Whites Cave (map 11, pl. 4). This 40-ft-long cave is shaped like an elongate dome. The highest point on the ceiling (11 ft) is at the cave's center; from here, the roof rounds down rapidly in all directions. Well-preserved lavacicles and dripstone line the surface of this dome. You enter the cave through a small opening where collapse debris spilled onto the floor of the cave. Downstream from the toe of this slide the floor is a jam of jostled pahoehoe blocks produced by the lava's attempt to drag its already solidified crust beneath the sloping roof of the cave at the downstream end. Undoubtedly, the domal shape and its walls of congealed dripstone suggested the name "The Igloo."

The Igloo may have formed as a short distributary tube from the upper part of the main lava tube, or it may be a cupola in the main tube with its floor having formed by the crusting-over of a balcony fill of lava in the main tube. It is impossible to decide between these alternatives because there is no access to the continuation of the tube either upstream or downstream.

Beaconlight Cave

Beaconlight Cave (map 11, pl. 3) is large in girth but only 340 ft long. It consists of two chambers: an entrance cavern 150 ft long, 50 ft wide, and as much as 35 ft high; and a larger chamber downstream, the Silver Clouds Cavern, which is 190 ft long and in places more than 50 ft high. Silver Clouds Cavern appears offset about 55 ft to the right (southeast) from the entrance cavern. A short arch 30 ft across connects the present roof of the two caverns above a high talus pile.

From the large alcove in the south corner of the Silver Clouds Cavern, a 10-ft-wide break in the floor spills a steep slide of collapse rubble into a lower tube 12 ft below. This deeper tube is 20 ft wide and 8 ft high; it trends almost due east for about 30 ft, and it has retained outstanding examples of pahoehoe floor, dripstone walls, and lavacicle roof. Only 50 ft downstream from the base of the slide, this tube is demolished by a slide of massive amounts of red breccia through its roof. At its northeast end the Silver Clouds Cavern terminates downstream where it plunges east into a lower level, but this lower tube is inaccessible because of lava accreted to its walls.

The name "Beaconlight" was given to this cave by J.D. Howard, after the Modoc Indian practice of illuminating the interior of caves in the search for water by building a row of bonfires of sagebrush inward from the entrance. Water does stand for a part of the year in the deepest part of the Silver Clouds Cavern, and also in a low spot in the lower tube. The name "Silver Cloud" derives from irregular patches of off-white caliche covering part of the roof of this room—when wet after seepage from rain, the caliche reflects light with a silvery glow.

Beaconlight Cave is the partly collapsed remnant of a large lava tube. Little of the original walls and virtually none of its ceiling have survived the slow unraveling of blocks loosened by frost action. Thick collapse rubble covers almost the entire floor of the cave except for a short stretch in the lower and smaller tube. Retreat of the walls by collapse provides good exposures of thin flow units in the thick lava flow in which the upper large tube developed. In the lowest parts of the two upper rooms this thick flow of lava rests in a few places upon a red breccia, which appears to completely encompass the lower small tube. The red breccia may be the underground extension of the tuffs and breccias, which make up the Schonchin Butte cinder and agglutinate cone (see map 12, pl. 4 and the "Skull Cave" section).

The most interesting geological area in Beaconlight Cave is the northeastern end of the Silver Clouds Cavern. The chamber narrows, turns abruptly almost due east, and plunges steeply into a lower level through an inclined tube 20 ft in diameter. This tube cannot be entered because it is blocked by many accretionary linings (each the remnant of a tube-in-tube) along the east wall, and because it is filled with collapse rubble on the west side. This downslope termination of a lava tube by accretionary linings is very similar to that of Arch Cave, Silver Cave, and to parts of Tickner Cave, except that it is larger and not as well exposed. Not all of the collapse rubble in Beaconlight Cave is of post-lava origin. At two places along the northwest and northeast walls of Silver Clouds Cavern, older collapse breccia was partly covered with dripstone of congealed lava.