Periods of calm, and suddenly large lava geysers that can reach hundreds of meters high: the volcanic eruption that has been ongoing for more than fifty days near Reykjavik, Iceland, offers a new spectacle, visible even from the capital.
If a security perimeter has been decreed to protect the curious from the dreaded shards of hot rock falling to the ground, many people still come to walk to the edge of the volcano, located in the Geldingadalir valley, near Mount Fagradalsfjall, at a forty kilometers from Reykjavik.
Evolution of the rash
Until then continuous and rather peaceful, the eruption – which will soon be officially baptized “Fagradalshraun” – has changed pace for a week, alternating periods of pauses and angry jets. An intense roar warns that the explosion is imminent, in this uninhabited sector of the Reykjanes peninsula, at the southwestern tip of Iceland.
Visible for tens of kilometers around, the bright orange geysers illuminate the sky, with ever shorter nights in this month of May. The national meteorological office estimates that one of the most intense spouts observed exceeded 460 meters high Wednesday in the early hours of the morning.
The lava cycle
These cyclical pulses are strangely similar to those of Strokkur, Iceland’s most active – water – geyser 100 kilometers east of Reykjavik. In fact, “magma is flowing all the time. It is just on the surface that there is a modulation, ”explains vulcanologist Magnús Tumi Gudmundsson.
“It’s normal behavior. It is, in fact, less common to have a very continuous flow without pulsation, ”he adds. The powerful lava bursts cause tephra fallout, rock fragments, some of which still hot – and potentially fatal – land several hundred meters from the crater.
The return of the lava
A permanent exclusion zone within a radius of 400 meters around the active crater has thus been established in calm weather and can be extended up to 650 meters depending on the wind speed. The eruption, which began on the evening of March 19, is exceptional in more than one way: it has been more than eight centuries since lava had flowed in the Reykjanes peninsula, and nearly 6,000 years ago where the rash has occurred.
Coming out of one then several faults, it formed several successive small craters in Geldingadalir – “valleys of the eunuchs” in French, only one of which is really active. Vulcanologists do not exclude any hypothesis on its duration, between a few additional months or even several decades.
“The rest is not entirely clear because the different types of volcanism that we have had on the Reykjanes peninsula can cover this entire time interval,” explains Edward Marshall, a geochemist at the Institute of Earth Sciences. One certainty, however, explains the specialist: “it is the most primary lava (directly from the earth’s crust, editor’s note) that we have observed since the last ice age”, which ended around 10,000 years ago.