What Is A Grímsvötn Volcano?

Grímsvötn volcano is located near the center of the Vatnajökull ice cap in central Iceland. At a height of 5658 feet, it has the highest eruption frequency of all the volcanoes in Iceland. Grímsvötn volcano has a complex of calderas, of about six by eight kilometers in area, and a subglacial caldera lake sustained by geothermal heat. A caldera, a large, circular depression at the summit of a volcano, is formed when magma is withdrawn or erupted from a shallow underground magma reservoir. The caldera lake is covered by a two-hundred-meter thick ice cap. Beneath the lake is where the magma forms for the Grímsvötn volcano.
Grímsvötn is considered a cinder cone volcano, which is the simplest type of volcano. A cinder cone volcano is built from
particles and drops of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and falls as cinder around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings.
Grímsvötn is the central structure on the long set of the trending fissures. The Vatnajökull ice cap, covers around eight percent of the landmass of Iceland. As well as Grímsvötn, the ice cap covers at least six other subglacial volcanoes. Each of the volcanoes are part of a volcanic fissure system crossing the whole area. The most prominent is the Laki fissure swarm, which, during an eruption in 1783, produced the world’s largest known historical lava flow.
Eruption frequency of the Grímsvötn center during the past centuries have been close to one eruption per decade. Small eruptions have occurred at the volcano in 1983 and 1998. In late October of 2004, earthquake activity at Grímsvötn increased. On October 26, high frequency seismic tremor indicated increased water flow from the caldera lake, signifying that a glacier outburst flood, or jökulhlaup, was about to occur. On October 29, discharge increased in the river Skeidara. The outburst flood was caused by high water level in the Grímsvötn caldera lake, from ice melting due to geothermal activity. The release in overburden pressure associated with the jökulhlaup triggered the eruption.
The latest and most recent eruption began on May 21, 2011 when plumes of ash shot into the air.
The explosive nature of the eruption was due to the interaction of hot magma with ice and water, producing ash particles. Multiple earthquakes indicated that magma was on the move. The ash cloud reached a height of twenty kilometers (twelve miles), cancelling more than nine hundred flights. The Grímsvötn volcano eruption was ten times larger than the 2004 eruption but did not disrupt nearly as much air traffic as the 2010 eruption on the island. The eruption released two thousand tons of ash per second during the first forty-eight hours of the eruption. The ash particles were much coarser than the eruption the previous year on Iceland. Reykjavik, the capitol, which is only one hundred and twenty miles from the volcano had large amounts of ash rain down on the city. The ash was so thick in parts of the island that it turned day into night. It was the most powerful eruption of Grímsvötn since 1873.
Grímsvötn’s volcanic active is said to be periodic. Active periods lasted from about one hundred to one hundred and fifty years ago with more restful periods of a few decades in between. However, with the eruption in 1983, an increased activity has started. Scientists believe that new magma is moving into the system. It is believed that the four eruptions in the last fifteen years indicate the beginning of an active period of volcanism on the island is beginning. New eruptions can be expected every two to seven years if the information provided by the scientists is
true.