Iceland is an unusual center of volcanic activity in the North Atlantic Ocean. It is the only place on Earth where a mid-ocean ridge occurs above sea level. Iceland's volcanism turns out to be related to both seafloor spreading and hotspot activity.
Below is a ~3000 year-old reddish scoriaceous basalt from the Kerith Crater (Keriš Crater) (see photo), a maar volcano in southwestern Iceland. Maar volcanoes are subcircular depressions with a subdued, low profile, and are typically filled with water. They form as a result of a steam explosion, the result of groundwater being superheated by overlying hot lava flows.
Scoria (8.0 cm across) from Iceland's Keriš Crater. The reddish coloration is from oxidation. Fresh, unoxidized scorias are dark gray to blackish-colored.