Lava Beds National Monument is located about ten miles south of Tule Lake, California, USA, just over the Oregon-California border. Comprising the northern side of Medicine Lake Volcano, the lava beds consist of 46,000 acres of lava tube caves, lava flows and fields, cinder and splatter cones, fumeroles, craters and fault scarps.
The area was designated a National Monument in 1925 by US President Calvin Coolidge and had over 28,000 acres named as a National Wilderness Area in 1972 by the US Congress. The area was also the site of the Modoc War of 1872-1873, where Modoc leader Kientpoos, also known as Captain Jack, with a group of 50 Modoc warriors including women and children, held off 300 US soldiers in a lava rock formation that was later known as Captain Jack's Stronghold. Indigenous habitation of the area can be traced back to about 6000 years ago in the form of pictographs and petroglyphs at three different locations within the monument.
Medicine Lake Volcano
The lava beds are part of Medicine Lake Volcano, the largest quaternary shield volcano in the Cascade Volcanic Arc. Similar to Newberry Volcano located south of Bend, Oregon, USA, Medicine Lake Volcano began forming about one million years ago during the Pleistocene era. The primary eruption began roughly 500,000 years BP in the form of tholeiitic alumina basalt, which covers most of the lower flanks of the volcano.
Subsequent eruptions of andesite are found at the higher elevations with rhyolite and dacite covering the areas around the caldera. The most recent eruption occurred approximately 1000 years ago to create Glass Mountain, an obsidian flow that sits on the eastern rim of the caldera. The flows that created the lava tube caves occurred roughly 30,000 years BP from Mammoth and Modoc craters. The basaltic lava from these flows comprise about two thirds of the rock that covers the lava beds.
Lava Tube Caves
One of the major geologic features of the lava beds are the lava tube caves that cover the monument. There are over 700 documented caves with 22 of them having been augmented with trails, stairs and lighting for easier access. Lava tubes are formed when highly fluid lava flows down a gradual slope and quickly cools. Coming into contact with the ground and air, the bottom, sides and top of the lava cool and solidify, creating an insulated channel that allows the inside rock to remain liquid. The lava eventually drains out leaving a hollow tube. Over time, weathering and erosion create openings in the tubes forming a system of caves that cover the lava field.
Two of the most interesting caves, Crystal Ice Cave and Fern Cave, are accessible by guided tours only. Crystal Ice Cave contains unique ice formations and is only open during the winter months. Fern Cave contains a remarkable display of pictographs and harbors a micro biotic climate that allows lush plant life to grow underground. Fern Cave is open from May to October. Other notable caves include Skull Cave, Big Painted Cave, Blue Grotto Cave and Golden Dome Cave.
Cinder Cones & Splatter Cones
There are numerous cinder cones throughout the lava beds that have formed over the past 500,000 years. One of the most prominent is Schonchin Butte. The cone was created from an erupting vent around 30,000 years BP. Frothy lava and ash were spewed into the air where it cooled and solidified in scoria. These bits of cinder and ash began to build up around the vent creating the cone. The Butte has a trail and fire lookout that was built between 1939-1941 by the Civilian Conservation Corps and is still in use today.
Splatter cones such as the Castles and Fleener Chimneys are not as symmetrical in shape as cinder cones. These vents spew out large globs of lava that fall haphazardly around them to create irregular mounds and chimneys. The Fleener Chimneys were formed around 10,500 years BP and produced a large flow that is now the Devil's Homestead lava field.
Pahoehoe and Aa Flows
Two different types of lava flows are evident at the monument. The Mammoth Crater flow is by far the largest and covers the widest expanse. The lava from this flow, known as Pahoehoe, moves in smooth, billowy waves and tendrils. The outer surface often cools and solidifies quickly, while the inner core remains liquid and spreads through tubes and channels to cover a wide area
The Fleener Chimney flow is made up of Aa lava, which is comprised of rough blocks of hardened lava covering a dense liquid core. This type of flow tends to tumble and roll as it moves, creating a sharp, rocky surface when it cools. The Devil's Homestead lava field provides an excellent example of this type of flow.
Volcanic Threat Assessment
The volcano at Medicine Lake is considered to be dormant at the present. However, it has one of the highest eruptive frequencies of any volcano in the Cascade Volcanic Arc with the most recent eruption occurring around 1000 years ago. In 2007, the US Geological Survey (USGS) designated Medicine Lake a "High Threat Volcano" with a high probability that in an active state it could erupt for decades (Donnelly-Nolan et al. 1). Flanked by Lassen Peak to the south, Mount Shasta to the west and Mount McLoughlin to the north, Medicine Lake is a slumbering giant that could become active again in our lifetime.
Sources:
Medicine Lake Vicinity, US Geological Survey, Topinka, L; Jun 2009
Lava Beds National Monument, National Park Service, US Department of the Interior; Mar 2011
Donnelly-Nolan, et al. Volcano Hazards Assessment for Medicine Lake Volcano, Northern California US Geological Survey, Reston, Virginia: 2007
Global Volcanism Program, Smithsonian, National Museum of Natural History: Dec 2010
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