Iceland hotspot in the context of Katla volcano

In geology, hotspots (or hot spots) are volcanic locales thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Examples include the Hawaii, Iceland, and Yellowstone hotspots. A hotspot's position on the Earth's surface is independent of tectonic plate boundaries, and so hotspots may create a chain of volcanoes as the plates move above them.

There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The alternative plate theory is that the mantle source beneath a hotspot is not anomalously hot, rather the crust above is unusually weak or thin, so that lithospheric extension permits the passive rising of melt from shallow depths.

A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hotspots, such as Hawaii or Iceland, and large igneous provinces such as the Deccan and Siberian Traps. Some such volcanic regions lie far from tectonic plate boundaries, while others represent unusually large-volume volcanism near plate boundaries.

The Rum layered intrusion is located in Scotland, on the island of Rùm (Inner Hebrides). It is a mass of intrusive rock, of mafic-ultramafic composition, the remains of the eroded, solidified magma chamber of an extinct volcano that was active during the Palaeogene Period. It is associated with the nearby Skye intrusion and Skye, Mull and Eigg lavas. It was emplaced 60 million years ago above the Iceland hotspot.

Krafla (Icelandic pronunciation: [ˈkʰrapla] ) is a volcanic caldera of about 10 km (6.2 mi) in diameter with a 90 km (56 mi) long fissure zone. It is located in the north of Iceland in the Mývatn region and is situated on the Iceland hotspot atop the Mid-Atlantic Ridge, which forms the divergent boundary between the North American Plate and the Eurasian Plate. Its highest peak reaches up to 818 m (2,684 ft) and it is 2 km (1.2 mi) in depth. There have been 29 reported eruptions in recorded history.