Rootless cone

A rootless cone, also called a pseudocrater, looks like a volcanic crater but it is not a real one. Rootless cones are not where lava comes out from deep under the ground. They form when hot lava flows over wet ground, like a swamp, a lake, or a pond.

When lava touches water, steam can explode. These explosions break through the lava and shoot out bits of rock and ash, called tephra. Over time, these bits build up and make shapes that look like real volcanic craters.

Some well-known rootless cones are in Iceland, such as the ones in Mývatn lake or the Rauðhólar near Reykjavík. Scientists have found similar features on Mars where old lava flows met groundwater. In March 2010, volcanologists watched a rootless cone form during the early part of the first eruption of Eyjafjallajökull.

Images

Here are some pictures of rootless cones found on Mars. These cones form when hot lava flows move over areas with water or ice. The water turns to steam and creates small explosions that shape the ground into rings or cones.

The images were taken by cameras on the Mars Reconnaissance Orbiter, showing different groups of these interesting landforms. Some cones look like chains, and others have strange shapes because the lava moved very fast.