“The lava field has not expanded in a few weeks, and the lava has not spread to new lands,” says Magnús Tumi Guðmundsson, professor of geophysics at the University of Iceland, referring to the eruption of the Fagradalsfjall volcano in southwestern Iceland.
“There are times when the lava does not flow at all and the lava channels close. The flow at the surface then resumes. Lava flowing on the surface cools down faster. It reaches the Meradalir, Geldingadalir and Nátthagi valleys but stops before reaching the edge [pola lawowego]. It piles up near the crater and builds up what looks like a shield volcano. ‘
Magnús Tumi explains that when the flow of lava is constant, it tends to flow beneath the surface. As a result, it cools slowly and can travel longer distances.
You can clearly see that the level of lava inside the crater drops significantly between eruptions. Using a drone, Jón Steinar Sæmundsson of Grindavík took pictures of the crater in July, when it was inactive. The attached photo is published thanks to his courtesy.
“The pictures show that the crater is very deep and leads a deep drain downwards from it” – explains Magnús Tumi. When the lava flow stops completely, the pressure drops as well. Apparently, it happens suddenly and the crater is completely emptied. After the flow has resumed, it takes many hours for the crater to fill again and the lava to flow out again. “
The crater basin is about 60–70 m deep, and the outflow from it goes much deeper. The measurements show that when the crater is inactive, the lava surface in the channel drops below the ground, as it was before the eruption.
New data on the size of the lava field are not available as weather conditions in recent weeks made it impossible to take aerial photographs. The last measurements were made on August 8. Cloud heights must be at least 2,000 m to be able to take pictures from which the lava field size is calculated.