A thousand quakes but no erupting lava

04.10.2021 - 11:42
Mynd með færslu
 Mynd: Vilhjálmur Þór Guðmundsson - RÚV
New data show that no new lava has flowed from the crater at Fagradalsfjall since the 18th September, making it the longest pause in activity since the eruption started—though glowing lava has been seen in the area, specialists say it did not come from the crater recently but is instead moving around within the new lava field. The lava field has sunk by 5-7 metres at its northern end and risen to the south in Geldingadalir and Nátthagi.

While the flow of lava has stopped from the crater, the flow of lava within the lava field has been around one cubic metre per second. Such redistribution of molten lava is quite well-known in lava eruptions.

The eruption can be split into five distinct periods that started with two weeks of steady lava flow of around six cubic metres per second. 

This was followed by another two-week period in which new fissures opened to the north of the original one and the flow rate was variable between around five and eight cubic metres per second. The lava flowed variously into Geldingadalir, Meradalir, or Nátthagi. 

The next phase was steady lava flow for around two-and-a-half months of 12 cubic metres per second; also flowing variously into Geldingadalir, Meradalir, or Nátthagi. 

Volatile activity directly related to magma flow below the surface started in late June, when lava flow started varying wildly from 8-11 cubic metres per second, with extended pauses.  

The latest stage may or may not be the closing stage; as in September there was a total stop in the eruption from the 2nd to the 11th, then a week of excited activity until the 18th, followed by another long pause that is ongoing today. 

It is as yet unclear if the fifth stage will be the extension of the lava intrusion to the north and the start of a whole new volcanic eruption. This scenario is now believed somewhat more likely than the other explanation that the earthquake swarm is simple tectonic readjustment in the area. 

Around a thousand quakes have been measured around Keilir in the past day. The biggest was magnitude 3.5, yesterday lunchtime. There was a 3.4 quake yesterday afternoon, a 3.0 just after 02.00 this morning, and a 3.3 this morning at 07.17. 

The earthquake swarm has now been ongoing for a week and has included 12 quakes over magnitude 3 and as many as 6,000 smaller quakes. The largest so far was a M4.2 on Saturday, which was widely felt in Southwest Iceland. 

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