DESCRIPTION:
Lava Tubes and Lava Tube Caves

During long-lived eruptions, lava flows tend to become "channeled" into a few main streams. Overflows of lava from these streams solidify quickly and plaster on to the channel walls, building natural levees or ramparts that allow the level of the lava to be raised. Lava streams that flow steadily in a confined channel for many hours to days may develop a solid crust or roof and thus change gradually into streams within lava tubes. Because the walls and roofs of such tubes are good thermal insulators, lava flowing through them can remain hot and fluid much longer than surface flows. Tube-fed lava can be transported for great distances from the eruption sites. For example, during the 1969-74 Mauna Ulu eruptions at Kilauea, lava flows traveled underground through a lava-tube system for more than 7 miles long to enter the ocean on five occasions.

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 coninue to drain downhill and may ultimately leave an open lava-tube cave -- often large enough for people to walk through.

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Ape Cave, Mount St. Helens National Volcanic Monument
-- U. S. Forest Service Image, courtesy Mount St. Helens National Volcanic Monument

Ape Cave is one of numerous lava tubes formed in the Cave Basalt. The basalt consists of pahoehoe flows that originated on the southwest flank of Mount St. Helens and flowed down the surface of older pyroclastic-flow deposits. Charcoal samples from two localities under the lava tubes yielded Carbon-14 ages of 1,860+/-250 and 1,925+/-95 years (Greeley and Hyde, 1972).

Ape Cave lava tube ... is the longest lava tube (12,810 feet or 3.9 kilometers) in the conterminous United States (similar tubes are found in Oregon, California, and Idaho) and one of the longest in the world. The cave was constructed by a pahoehoe flow that crusted over; soon after, the molten lava on the inside drained away, leaving the outer crust in place. Lava stalactites and stalagmites and flow marks can be seen on the walls and floor of the cave. Lava stalactites, conical or cylindrical deposits of lava that hang from the ceiling of a tube, are formed by dripping; stalagmites are similar in shape and are formed on the floor of the tube by the accumulation of drips from the ceiling. ...

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The Indian Heaven volcanic field is midway between Mount St. Helens and Mount Adams ... Basalt to mafic andesite lava flows range from 0.4 to 24 meters in thickness, whereas andesite flows are up to 90 meters thick. Individual flows extend up to 46 kilometers in length, have areas to 116 square kilometers, and volumes to 1.2 cubic kilometers. Most flows less than 150,000 years of age contain extensive lava tubes, making the Indian Heaven Volcanic Field and important speleological area.

The Indian Heaven volcanic field, midway between Mount St. Helens and Mount Adams, is a Quaternary center, chiefly of basalt. ... About 60 eruptive centers lie on the 30-kilometer-long, N10degreesEast-trending, Indian Heaven fissure zone. The 600 square kilometer field has a volume of about 100 cubic kilometers and forms the western part of a 2000-square-kilometer Quaternary basalt field in the southern Washington Cascades ... Pahoehoe and a'a typify the basalt flows; some of the andesite is block lava. Tephra production was minimal, although the basaltic tephra accompanying extrusion of the Big Lava Bed flow has a volume of about 100,000 cubic meters. Big Lava Bed is known for its tubes and for the remarkable microtopography on its surface, which mostly results from inflation of the flow when its feeder tubes clogged.

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Halfway between Bend and Sunriver, the geologic wonders of Newberry National Volcanic Monument start to unfold. First and most obvious is Lava Butte and the Lava Lands Visitor Center. ... One mile south from Lava Butte, Lava River Cave is Oregon's longest intact lava tube. You can explore this mile-long phenomenon with lanterns and flashlights, warm clothes and good walking shoes.

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During the 1969-74 Mauna Ulu eruptions at Kilauea, lava flows traveled underground through a lava-tube system for more than 7 miles long to enter the ocean on five occasions.

Link to: Hawaiian Volcano Observatory Website for MORE Information

Lava Beds National Monument is located in northeastern California about 50 kilometers south of Klamath Falls, Oregon. The monument, established in 1925, includes the sites of many important battles of the Modoc Indian War of 1872-73. It is also known for scores of lava-tube caves and for well preserved young volcanic features. ... The basalt of Mammoth Crater is the dominant unit in the monument in terms of area and volume and is host to most of the nearly 300 lava-tube caves. ...

Lava Beds National Monument lies on the north slope of the huge Medicine Lake shield volcano, a complex volcanic edifice of greater volume than the steep-sided Mount Shasta volcanic cone, which towers as a snowclad landmark 40 miles southwest of the monument. 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 coninue to drain downhill and may ultimately leave an open lava-tube 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. 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 miles from their sources. Nevertheless, today one cannot walk for a distance of even 4 miles 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.

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