The Kerguelen Plateau in the Indian Ocean is the world’s longest continuously erupting supervolcano dating back into the Cretaceous, according to research published in the journal Geology. This discovery is quite exceptional, considering that these types of eruptions typically last just 1-5 million years.
For over 30 million years, from around 122 million years ago to 90 million years ago, basaltic lava erupted from fissures on the seafloor building up a volcanic plateau, eventually breaking sea level. The presence of soil layers in the basalt which included charcoal from large trees, indicate that much of the plateau was above sea level between 100 million years ago and 20 million years ago. In the last 20 million years, the volcanic edifice started to sink slowly and is now 1,000–2,000 m (3,300–6,600 ft) below sea level, with the exception of the Kerguelen Islands (today a French overseas territory) and the Heard and McDonald Islands (an Australian external territory).
One of the largest igneous provinces (LIPs) in the world, the Kerguelen Plateau covers an area of 1,250,000 km2 (480,000 sq mi) – an area half the size of the continent of Australia – and rises 2,000 m (6,600 ft) above the surrounding oceanic basin.
Every LIP is connected to a hot-spot, a stationary region where plumes of hot material are upwelling in Earth’s mantle. The plume causes partial melting of the uppermost parts of the mantle and the crust, providing so the quantities of magma needed to feed the superficial lava eruptions. The Kerguelen Plateau was produced by the Kerguelen hotspot, starting with or following the breakup of Gondwana about 130 million years ago. Intermittent volcanism continues to this day on the Heard and McDonald Islands.
Using the decay rate of radioactive minerals found in the basaltic rocks, the researchers dated 25 drill cores recovered from the plateau. Volcanic activity peaked between 122 to 90 million years ago, depositing 7.87 inches of lava a year on the seafloor, enough fresh lava to fill 184,000 Olympic-sized swimming pools. After this initial phase, the eruption rate decreased significantly, remaining low to this day.
The Kerguelen Plateau saw such a long and steady run of volcanic activity because of its unique configuration, the study suggests: a mantle plume combining with an active mid-ocean ridge. The Indian Ocean is crossed by three mid-ocean-ridges, the outer limits of three large tectonic plates, including the African, the Antarctic and Australian plate. Until a few million years ago, the Kerguelen Plateau was located exactly above a hot-spot sitting along the mid-ocean ridge between the Antarctic and Australian plate.
Other hot spot volcanism will eventually stop erupting because, when temperatures cooled, the feeding dikes became clogged by solidified magma. For the Kerguelen Plateau, the mantle plume provided the necessary energy to melt the rocks, as tectonic movements along the spreading mid-ocean ridge kept the dikes open, which successively acted as a ‘magma conveyor belt’ for more than 30 million years.