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Lava Flows and Domes at Medicine Lake Volcano

Basaltic to andesitic lava flows and associated cinder cones and spatter cones are the dominant types of eruption at Medicine Lake volcano.

Map showing Medicine Lake volcano lava flows 100,000 years old and ...
Postglacial lavas ~13,000 years old and younger are shown in darker pink. Major lava flows are labeled, including anr (andesite of north rim) and asr (andesite of south rim). Five very large basalt lava flows are also labeled: bgc = basalt of Giant Crater, bmc = basalt of Mammoth Crater, byb = basalt of Yellowjacket Butte, bl = Lake Basalt, and bt = basalt of Tionesta. Flow directions are indicated by arrows on the five large basalt flows.

Such eruptions could occur anywhere on the volcano, and lava could potentially erupt from multiple vents distributed along fissures as long as 15 km (9.3 mi). Basalt lava is more fluid (less viscous) than andesite lava and a single flow can cover an area up to >300 km2 (115 mi2). Due to greater viscosity, andesite and basaltic andesite lava flows are typically limited in length to less than 12 km (7.5 mi) and cover areas less than 25 km2 (9.6 mi2.

The largest basalt flows at Medicine Lake Volcano erupted during the most recent fifth of the volcano's existence. The youngest of these very large basalt flows is the postglacial, 12,500-year-old Giant Crater flow, which covers about 200 km 2 and flowed 45 km (28 mi) south from its vents on the volcano's south flank. Eruptions such as that probably continue for months or years. The broad apron formed by the extensive basalt flows establishes a perimeter that is not likely to be exceeded by future flows. Nonetheless, it is possible that a future basalt flow could advance beyond this limit. If lava should flow into Tule Lake, localized explosive activity would occur where hot lava meets water.

Eruptions of dacite to rhyolite have also occurred in the volcano's past, but are only likely to occur near the summit and cover small areas. The viscous nature of silicic lavas such as these indicate that years to decades could elapse during such an eruption. A summit-area lava flow within the caldera could potentially enter Medicine Lake and generate localized steam explosions.

The most likely future volcanic event at Medicine Lake Volcano would be a mafic eruption that built a cinder cone and produced a lava flow a few kilometers in length. However, prolonged silicic or basaltic eruptions lasting years or even decades are possible. Lava flows do not move very quickly and can be easily outrun, but they would damage or destroy any infrastructure in their path. During dry or windy weather, the advancing flow front of any lava flow on the volcano would likely cause fires.