Subsidence in Iceland, a strange relationship.

Iceland doesn't have to worry about subsidence. Well, not in the usual sense. Soil subsidence is the movement of surface material, generally due to a change in conditions below the surface. A thick layer of soil above limestone, for example, can produce large movements of surface material, including sinkholes, when the underlying limestone is dissolved by weakly acidic water. Iceland has very little sedimentary rock (8-10%), and no large areas underlain by soluble rock. Rock history of iceland. The subsidence Iceland does have to worry about however, relates to volcanoes.

The image above is of the massive Bárðarbunga eruption from 2014-2015. This volcano erupted continuously for five months, from Sept. 2014 to Feb. 2015. In this time, and in the time since, the area inside of Bárðarbunga's caldera (the opening of the volcano) sank over 35 meters (115 feet) as the magma chamber emptied itself into a massive lava field on the surface. Detailed report of Bardarbunga caldera subsidence. The total subsidence for this event (the detailed measurement did not begin until the event had already started) is estimated at nearly 60 meters. The graph below shows this subsidence from Sept.-Mar. The eruption ended in mid February, and you can see that as the subsidence ceased, the line reversed very slightly. This shows that almost immediately upon cessation the magma chamber began to fill again.

Measuring the swelling or subsidence inside of volcanoes is a valuable tool for geologists trying to predict the health or volatility of a volcano. Subsidence during an eruption is self explanatory. If your volcano is subsiding with no visible eruption however, you must look for another reason, either that there is an eruption somewhere you can't see (such as into the sea or underground) or that the flow of magma which filled that chamber has gone elsewhere. If the flow of magma into a particular chamber does cease, a total collapse of the caldera may occur. This happened to the caldera of the Askja volcano after a massive eruption in 1875.  Askja caldera collapse. This particular event took over 40 years, and as such was not very dangerous, but a sudden collapse is possible and would pose a danger to any scientists unlucky enough to be studying the area at the time.