There are many indications that the eruption on the Reykjanes peninsula in southwestern Iceland, which began last Friday, may create a shield volcano. Volcanoes of this type have not been formed on Earth since the end of the Ice Age.
Lava flow for shield volcanoes is generally slow, but can be very long – even years. Such a scenario cannot be ruled out for the current eruption of Fagradalsfjall in the Geldingadalur valley, states geologist Magnús Á. Sigurgeirsson. Magma flows out here at a speed of 5-10 m3 / s.
Among the known shield volcanoes on the Reykjanes peninsula is Þráinsskjöldur, formed around 14,100 years ago. Another such volcano, more famous, is Skjaldbreiður, northeast of Þingvellir National Park, formed 9,000 years ago.
(Skjald means shield in Icelandic).
Examination of volcanic products suggests that the magma flows from a depth of 17–20 km and is more primal than what we have seen before. By describing the magma composition as primary, geologists mean it resembles that of the mantle, explains Sæmundur Ari Halldórsson, researcher at the Institute of Geosciences at the University of Iceland.
The magma of Fagradalsfjall comes directly from the Earth’s mantle and flows out without lingering in the Earth’s crust. Therefore, its composition differs from the magma found in typical fissure eruptions on the Reykjanes peninsula – it is rarer and richer in carbon dioxide.
However, it is too early to say that the current eruption is indeed forming a shield volcano. It is necessary to monitor the outflow and track changes in the magma. Sæmundur points out that while the region is similar to large shield volcanoes, there are also smaller lava fields that contain equally primal chemicals.
The largest shield volcano discovered so far is Olympus Mons, located on … Mars. It is also the highest known peak in the solar system. Because the tectonics of the plates on Mars is rather in its infancy, the Martian crust is hardly shifting and subsequent volcanic eruptions occur at the same point. And the volcano grows, grows and grows, becoming the largest shield volcano ever seen by humans. The slopes of this volcano have a slight slope, but it rises more than 21 km above sea level (if there were still seas on Mars) and almost 27 km above the surrounding area – three Chomolungmas one on top of the other. Olympus Mons has a diameter of 624 km, and the cliffs on its edge are almost 6 km in places … This volcano has a surface that would cover Iceland as a whole.