Hotspots and Large-body Impacts

The Kilauea volcano on the Island of Hawaii is one of the most active volcanoes in the world and visitors come to see the orange rivers of glowing lava that flow usually very peacefully – though sometimes aggressively and destructively – from the craters and vents and pours in dramatic cascades into the spitting and steaming ocean. The Island of Hawaii also includes two much higher volcanic peaks, Mauna Kea and Mauna Loa, whose eruptive activity has continued until fairly recently.

All the Hawaiian Islands are products of volcanism and the reason for their continued activity is a phenomenon called a hotspot. Hotspots are thought to be plumes of rising heat through convection currents within the mantle. The earth has 40-50 identified major hotspots and many minor ones, too. Hotspots remain in a relatively fixed position and so as the plates drift over them their product volcanic edifices are moved away from the up-welling magma and the volcanoes become extinct while a new volcano is born over the hotspot. The Hawaiian Islands form a chain of volcanoes with the Island of Hawaii comprised of the most recently active volcanoes, Maui’s Haleakala having been active until the recent past, and all islands becoming older as one moves northwest. On the ocean floor, a chain of extinct volcanoes and former islands extends across the Pacific, makes a change of direction halfway to Asia and continues on to its subduction zone at the far western end of the Aleutian archipelago. Other famous hotspots include the Yellowstone Caldera and Mount Etna.

What exactly are hotspots and what causes them? Two theories are that they are either deep mantle plumes or shallow plumes. But a new hypothesis is being tested that would suggest the origin of at least some of earth’s hotspots is large-body impacts. According to the paper by Johnathan T. Hagstrum, most of the earth’s major hotspots have antipodal hotspots or large igneous provinces (LIPs) of roughly the same age. The paper examines evidence that could suggest that a bolide of greater than 20km diameter striking the earth in an ocean could penetrate into the mantle and disturb it enough to create long-term volcanic activity where eruptive magma would cover any evidence of the impact crater. Furthermore, such a large impact would create Rayleigh shock waves that would spread around the globe and converge at the antipode of the impact. This convergence of seismic energy could fracture the crust sufficiently so as to lead to eruptive activity. One significant point is that most hotspots have antipodal LIPs, which suggests that if a large-body impact created the hotspot then the seismic energy focused at the antipode possibly triggered the basalt floods that created the LIPs. Another point is that in the case of continental impacts, the tensile strength of the thicker continental crust acted as a shield that prevented the creation of an antipodal hotspot or basalt flood. Only very large continental impact sites have antipodal hotspots. The paper offers a lot to consider.

So how about our Hawaiian hotspot? Its antipode is Lake Victoria in Africa; however, the research paper says that some antipodal hotspots are just coincidental and in the Hawaii/Lake Victoria case this seems to be the situation.

For further reading:

Hotspots

Antipodal Pair Impact Hypothesis

A post of mine about meteor craters