Eruption’s New Behavior Explained

The eruption by Fagradalsfjall mountain, Southwest Iceland, never ceases to surprise scientists. “The eruption keeps changing its appearance without showing signs of being about to end,” Þorvaldur Þórðarson, volcanologist and professor at the University of Iceland, tells Morgunblaðið.

The latest development to surprise scientists is the eruption’s pulsating behavior since Saturday night. Magma jets from the crater now reach as high as 300 meters into the air, with pauses in between.

A likely explanation, according to Þorvaldur, is that the shape of the uppermost part of the conduit has changed. Possibly, a constriction has formed, affecting the upwelling of large gas bubbles. When they burst, the magma jets shoot into the air.

“We’ve also been thinking about Þríhnúkagígur and its characteristics,” states Ármann Höskuldsson, volcanologist and research professor at the University of Iceland. (Þríhnúkagígur crater is a dormant volcano in Southwest Iceland, which can be viewed from within. Special tours are offered there, called Inside the Volcano).

“Possibly, there is a tank under the crater – some sort of lava lake,” Ármann continues. “The crater is the spout of the lake and smaller than it in diameter. Hot lava comes up through the bottom, full of gas. The uppermost magma is somewhat colder and has rid itself of much of the gas. Then a turbulent flow occurs, bringing the gas-rich magma back up. Once it begins to boil, a backward pressure wave moves downward, the system is degassed and lets the magma jet out. The jets continue while the new magma is being degassed. Once that is over, the magma jet drops and the system starts recharging for the next shot.”

Ármann and Þorvaldur believe the magma flow has rather increased than decreased. There are signs of more water in the magma, which may be explained by hot lava having melted waterlogged strata. The more powerful magma jets suggest a higher water content in the system. So does the blue haze or smoke from the eruption, Ármann explains.