Faults actively participate in the evacuation of the internal heat of the Earth

Since its formation, the Earth evacuates its internal heat in a continuous way. In other words, she’s just getting colder. However, this transfer mechanism heat between the core and the surface is one of the fundamental processes that makes the Earth “alive” from a geological point of view. It is in fact the origin of the convection from coatwho is the main driver of plate tectonics. The movements continents, but also the perpetual growth of the oceanic crustas well as the associated volcanism and seismicity are therefore the witnesses, on the surface, of this great dissipation ofenergy.

Earth’s heat is released at ocean ridges

On the surface of the globe, the heat will be evacuated mainly at the level of the ocean ridgesor magmatic processes lead to the formation of new oceanic crust. This intense heat flow will give rise to strong hydrothermal activity, illustrated by the presence of large fireplaces spitting out a hot fluid charged with minerals.

These fluids are the source of seawater, which seeped into the oceanic crust. By circulating within the rocks, this sea water will gradually warm up and load up on various minerals, before rising to the surface at the hydrothermal vents. If it has long been assumed that this hydrothermal circulation is favored by the presence of active faultswith fluids using them as conduits through the crust, this interaction had not yet been clearly demonstrated.

To study the influence of active faults on hydrothermal circulation, a team of researchers went to investigate one of the only places in the world where an oceanic ridge outcrops at theair free: Iceland.

Iceland: a playground for understanding the interactions between faults and hydrothermalism

The researchers thus monitored the volcano-tectonic segment of Krýsuvík, where significant hydrothermal activity can currently be observed. In 2000, Lake Kleifarvatn, which is located in this region, had been drained for 16 months following a earthquake. The water had then seeped into the fractured basaltic crust, leading to a loss of 12% of the volume Lake. A dense network of sensors seismic data was therefore deployed in the area, in 2005 then in 2009, in order to record all seismic activity. Thousands of micro-earthquakes have thus been detected in hydrothermal regions.

During this time interval, the researchers thus observed a migration of fluids within the upper crust. While the 2000 earthquake initiated deep fluid penetration, data acquired between 2005 and 2009 suggest that the region is now subject to fluid upwelling. Microseismicity has in fact evolved from a deep zone (5-6 kilometres) to a very superficial zone. This tectonic activity is associated with a migration of an overpressure front caused by the rise of hydrothermal fluids. These data would therefore sign the development, in the space of a few years, of hydrothermal cells. The rise of hot fluids would therefore be controlled by the network of fractures present in the crust.

The periodicity of hydrothermal activity in relation to the seismic cycle

For the authors of the study published in the journal Communications Earth and Environment, so there is a major link between hydrothermal activity and tectonic activity. More precisely, it seems that the initiation of the hydrothermal cell within the basaltic crust is linked to a major seismic event that opened up a whole network of fractures allowing the infiltration of water at depth. Once heated, the fluids will rise during the interseismic period, promoting heat transfer to the surface. The seismic cycle therefore seems to play a very important role in the hydrothermal circulation and could help explain the periodicity of the hydrothermal activity observed in many tectonic contexts, in particular at the level backbones.