By combining data on gravity, chemistry and how seismic waves are reflected and scattered deep within the Earth, an international group of scientists affiliated with the European Space Agency (ESA) have created a model of Earth’s lithosphere , showing how cold and hot rock plumes move slowly there. .
The model combines different satellite data, such as gravity data from ESA’s GOCE mission, with seismic tomography, a technique using networks of seismograph stations on the Earth’s surface to map the behavior of seismic waves inside the Earth, and the chemical properties of rocks to create a virtual Earth. As a result, the model shows the temperature differences of the rock up to 400 kilometers deep. This area, called the lithosphere, includes the Earth’s outer shell and parts of the upper mantle and plays a vital role in driving plate tectonics.
The Earth’s outer shell or crust comprises seven major tectonic plates and several smaller ones. Rigid tectonic plates slide over a ductile layer, the astenosphere, pushed and driven by convection currents in the mantle. As parts of the tectonic plates are pulled into the mantle, they release water and melt, fueling explosive volcanism along the edge of the plate. One such example is the Hunga Tonga-Hunga Ha’apai Volcano.
Sergei Lebedev, from the University of Cambridge in the UK, co-author of the model: “This is part of the Tonga-Kermadec arc, where the edge of the Pacific tectonic plate dips below the Australian plate. Here our imagery shows the layer of hydrated and partially molten rock above the plunging plate from the Pacific, which feeds the volcanoes in the arc.The model shows the cold crustal fragments sinking in blue and the less dense hot rocks rising in red.
In other regions of the mantle, the model shows how large plumes of hot and cold material rise or fall, driven by temperature differences. the Cumbre Vieja volcano on the Spanish Canary island of La Palma is fed by the Azores plume, a large thermal anomaly in the upper mantle.
Scientists still don’t know what causes these thermal anomalies. Based on seismic data, large structures found along the core-mantle boundary at a depth of about 2,800 kilometers likely play a role. Here, convection currents push mantle materials together, forming plumes of less dense rock that will eventually rise and heat regions of the mantle.