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If you've been following the latest geological news, you'll have noticed the brand new eruption on Iceland's Reykjanes Peninsula. It's a classic example of an eruption of relatively fluid lava simultaneously at multiple points along a fissure in the earth, resulting in "curtains of fire". These fascinating phenomena provide a spectacular glimpse into the geologic processes driving eruptions.

Piles of globby black lava stretch out in a line into the distance of a sagebrush-covered desert landscape. In the distance, a broad shield volcano is surrounded by multiple smaller scoria cones. View is south toward the upper part of Medicine Lake volcano.
Small spatter vents of upper Ross Chimneys form part of the Black Crater-Ross Chimneys basalt flow (map unit bbr) that erupted about 3,000 years ago in the northern part of Lava Beds National Monument. The numerous spatter vents are aligned along a north-northeast trend. View is south toward the upper part of Medicine Lake volcano. USGS photo by Julie M. Donnelly-Nolan.

Why do these eruptions happen? When magma rises to the surface of the earth, it often takes the form of a dike, or a vertical slab that fills in space between two blocks of the earth's crust. This can be taking advantage of an existing fault, or the dike can form its own crack. If the dike reaches the surface along a length of this crack, lava can erupt at multiple spots at the same time, fountaining into the air as it's driven out by gases (see the NPS diagram below). Spatter from these fountains builds ramparts, or banks, along the fissure, further channeling the eruption into a narrow line. This most often happens with fluid lava like basalt or basaltic andesite. These eruptions don't necessarily release a lot of lava - the resulting flows may only travel a short distance from the vent - but they are spectacular to see.

Diagram showing the origin of fissure volcanoes from dikes intersecting the surface and feeding lava flows. In a cutaway block of the earth's crust, a thin red vertical slab of magma is labeled to indicate upward movement. Its intersection with the surface is marked with fissures in bright orange, accompanied by a drawing of an erupting spatter cone and lava flows, all within a shallow faulted basin.
Graphic by Trista Thornberry-Ehrlich (Colorado State University) after Hughes and others (1999) -- Mafic Volcanism and Environmental Geology of the Eastern Snake River Plain. National Park Service graphic from

Iceland's eruption is just the latest example of a curtain of fire. But there are also places in California where the same kinds of eruptions have happened - they're just a bit older! Medicine Lake volcano in northern California also produced fissures about 3,000 years ago, at the Black Crater and Ross Chimney vents in Lava Beds National Monument (first photo). These basaltic vents are scattered along a 2.5 km (1.6 mi) long fissure, and built up spatter ramparts as well as some small lava flows. If you had been around 3,000 years ago, this eruption would have looked very similar to the one happening in Iceland right now!

To learn more about Medicine Lake's eruptions, check out

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