An international research team led by a Russian geophysicist from Novosibirsk State University and Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, Ivan Koulakov has explained the unusual behavior of the Toba supervolcano in Indonesia. Nature Communications published a research report of the team, which is based on a new seismic model of the magma paths beneath the volcano, on Tuesday, 19 July, 2016.
“The Toba supervolcano located in northern Sumatra has been the site of 3 hazardous explosive eruptions over the past million years. The most recent Toba supereruption occurred about 74,000 years ago. It is considered to be the largest terrestrial volcanic eruption of the Pleistocene. During the eruption, the volume of the material erupted was as high as about 2,800 km3. This terrible catastrophe caused a dramatic climate change affecting all the Earth,” says Dr. Ivan Koulakov, the Head of seismic laboratories at Novosibirsk State University and the Institute of Petroleum Geology and Geophysics. “If such an eruption occurred in modern times, it would drastically alter the life of human species. An insight into functioning of the system that periodically produces supereruptions seems to be of paramount importance.”
“Strange though it may seem, water is the most explosive material on the Earth. The deadliest volcanic eruptions were caused by sudden transformation of overheated water to gases inside underground reservoirs. It is not so much lava that is dangerous, but powerful explosions caused by the water beneath the volcano. Thus, water transfer inside the Earth affect the intensity of volcanic eruptions,” says Ivan Koulakov.
Toba the supervolcano is located in the Sunda subduction zone, where the Indian oceanic plate sinks beneath the continental lithosphere of Sumatra. Toba’s remarkable feature among other subduction-related volcanoes is its unusually strong explosive eruptions, which occurred in the same location with the intervals of several hundred thousand years.
The scientists report that the major cause of such a behavior is associated with a large fracture zone along the Investigator Ridge in the Indian Ocean, which subducts right underneath Toba. This fracture zone accumulates a large amount of water and brings it to the mantle. The amount of water is several times as high as in the case of a regular subduction zone. At a depth of ~150 km, the water escapes from the slab and starts ascending through the mantle wedge. At this stage, it reacts with the mantle rocks and lowers their melting temperature. Then an intense flow of melts and fluids ascends to the bottom of the crust. Due to a relatively high density, the mantle rocks cannot further ascend through the crust and form a large magma reservoir at the bottom of the crust with the volume estimated 50,000 cubic km.
This reservoir functions as a huge heater and a source of fluids. The upward migration of overheated fluids is a very effective way of heat transfer, which causes rock melting in the upper crust and another reservoir forms at depths of 7-15 km. Only when the magma reservoir reaches a critical level of overpressure due to the trapped volatiles, the reservoir empties and the large amount of magma begins to rise through the crust, eventually leading to a large-scale explosion.
As long as the Investigator Fracture Zone subducts underneath Toba and brings anomalous amount of water into the reservoir in question, this “steam engine” will continue working and producing periodic catastrophic eruptions. However, the scientists are not jumping to doomsday conclusions. “Although another extremely large eruption is likely to happen in future, there is no evidence to suggest that the eruption is imminent,” says Ivan Koulakov.
Последняя редакция: 26.08.2016 10:09