Lava Beds National Park is located in eastern Siskiyou County, far-northern California, USA. It is a world-class place for observing Pleistocene-Holocene mafic volcanic features. The main volcanic features and lava flows at Lava Beds range in age from ~2 million years to ~1100 years (Late Pliocene to late Holocene).
The Lava Beds area is dominated by somewhat weathered mafic aa and pahoehoe lava flows. Eruptive centers are usually obvious and form prominent hills or mounds.
There's also an abundance of lava tube caves in the area that can be entered and explored, although only one has had lights installed by the park service.
GILLEMS BLUFF FLOW
A prominent bluff is present near the northern entrance to Lava Beds National Park. This is a fault-uplifted block of lava belonging to the Gillems Bluff Flow. At ~2 million years (Upper Pliocene), the Gillems Bluff Flow is the oldest lava at the surface in the Lava Beds area.
Looking ~SSW. The Gillems Bluff Flow is the cliff at the right.
Mushpot Cave is an easily accessible lava tube cave near the visitor's center at Lava Beds, California that has a paved trail & electric lights. Lava tube caves represent former shallow-underground conduits for hot, flowing lava. Lava tubes can be seen forming today at the Hawaii Hotspot, in association with Mt. Kilauea's ongoing lava eruptions.
In general, the accessible portions of Mushpot Cave have a slightly flattened circular cross-section. At one time, this cave had >2000° F basaltic lava flowing through.
The level at which lava flowed did vary. The former lava levels are generally represented by lines along the cave wells, analogous to bathtub rings.
The ceiling of Mushpot Cave, and most other lava tube caves, has distinctive “stalactite” structures. These are lavacicles. They formed when the tube was only partially filled with flowing lava. The ceiling rocks began to melt and dripped downward from the heat of lava flowing underneath.
The heat of flowing lava also affected the walls of lava tubes. Below is a photo showing a pullout structure, or lining rupture. The heat of flowing lava weakened the lining of the tube walls, resulting in a section of lining peeling away, or pulling out, from the wall.
Mushpot Cave is so named after the structure depicted in the photo above. This is a mushpot structure. It is claimed to be the only example of this volcanic feature anywhere in the world. It is located immediately adjacent to stairsteps at Mushpot Cave's entrance.
Lava tubes can be seen to have tributary and distributary channels, just like rivers & streams with flowing water. The pic above shows a distributary lava tube within the Mushpot Cave lava tube.
Chocolate Cave is another of a series of lava tube caves at Lava Beds, California. The entrance area consists of a natural arch formed between two sections of collapsed lava tube.
Chocolate Cave is named in reference to the rich brown coloration of the smooth-surfaced lavacicles abundant on the walls & ceiling.
MEDICINE LAKE VOLCANO
Medicine Lake Volcano (see pic) is a shield volcano in far-northern California, USA. It is associated with the Cascade Range of stratovolcanoes. The Cascade Range formed by subduction of the Juan de Fuca Plate underneath the North American Plate in northern California, Oregon, Washington State, and southwestern British Columbia. Quite a variety of material has been erupted from the Medicine Lake Volcano, including basalts, andesites, rhyolites, dacites, obsidian, and pumice.
The rocks shown below are airfall pumice pieces from a ~1065 A.D. eruption at the Glass Mountain eruptive center, on the eastern side of Medicine Lake Volcano.
Above: airfall pumice pieces from ~1065 A.D. eruption of Medicine Lake Volcano. Pale-colored pumice at upper right is 2.7 cm long.
Mammoth Crater is located at the southern boundary of Lava Beds Park. It erupted at about 35 ky, in the Late Pleistocene. Lava flows from the Mammoth Crater Cinder Cone cover most of the Lava Beds area. Most of the lava tube caves in the area are developed in the Mammoth Crater Flow.
Above: Mammoth Crater Cinder Cone's vent area. Looking ~N.
Above: Looking down into Mammoth Crater's vent. The loose igneous debris is vesicular & scoriaceous basalt.
Schonchin Butte Cinder Cone
The most conspicuous eruptive center at Lava Beds is a tall cinder cone called Schonchin Butte. It is a classic cinder cone - a relatively small (for a volcano), steep-sided cone of mafic igneous debris. During the Late Pleistocene (65 ky), the Schonchin Butte Cinder Cone erupted lava toward the north-northeast. This particular lava flow is called the Schonchin Flow.
Black Crater Spatter Cone
The Black Crater Spatter Cone is a small eruptive center at Lava Beds. It erupted relatively recently, at about 1300 B.C. (3300 years ago; 3.3 ky). The Black Crater Flow extends principally to the north-northeast of the spatter cone.
Above: Black Crater Spatter Cone (3.3 ky). Looking ~E.
Above: Vent area of Black Crater Spatter Cone.
Above: Vesicular & scoriaceous basalt spatter (3.3 ky) along the walls of Black Crater Spatter Cone's vent.
Above: Black Crater Spatter Cone's vent. Looking ~ENE.
Above: Northern end of Black Crater Spatter Cone's vent. Looking ~NNE.
The four pics above & below show basaltic aa lava in the 3.3 ky Black Crater Flow. The cliff-like ridge in the distant background in the two photos below is Gillems Bluff, which exposes the ~2 my Gillems Bluff Lava Flow.
Devil's Homestead Flow
The Devil's Homstead Lava Flow is located along the western boundary of Lava Beds Park. It erupted at 12.8 ky (near-latest Pleistocene) from the Fleener Chimneys eruptive center. It consists of vesicular & scoriaceous basaltic aa lavas.
Looking ~SE. The hill in the distance at right is Schonchin Butte.