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.
Fall into a burning (curtain) of fire with fissure eruptions
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.
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 https://pubs.usgs.gov/pp/1822/pp1822.pdf
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