Subsidence/ Sinkholes

Subsidence is of great concern for volcanologists due to Iceland's unique landscape. The frequent volcanic activity of Iceland results in the island's issue of subsidence. Earthquakes also contribute to this. The risks of the subsidence being experienced on the island at the Bárðarbunga caldera. This is centrally located in what is known as the Holuhraun lava field. 
According to volcanologist Haraldur Sigurdsson, "the subsidence in the center of the Bárðarbunga caldera is an exponential function that will gradually slow down relieving the pressure in the volcanic system that supplies magma to the Holuhraun eruption," (Sigurdsson, Iceland Magazine). 

Fortunately, his prediction appeared to be correct as the eruption appears to be coming to an end as the pressure in the magma chamber is coming to a balance in this caldera. 
According to our text, "Subsidence can also occur from volcanic activity, related to either the central magma chamber of the volcano or shallow tunnels on the flank of the volcano. As magma moves upward into underground chambers below a volcano, the surface of the volcano may be forced upward. When it erupts, the volume of magma in the underground chamber is reduced and the land initially uplifted by the magma will subside," (Devecchio, Keller, p. 265). 

Bárðarbunga Caldera is beneath 600-850 meters of ice known as Vatnajökull glacier. The flow of lava can sometimes leave a void when the lava drains from what's known as the "lava tube" making it susceptible to collapse. Both are risks for Iceland. 
The depression in the ice above the Bárðarbunga caldera is the largest in Iceland recorded at more than 55 meters (180 ft.). Subsidence is occurring in other areas of this glacier as well so this occurance is not isolated to this caldera alone. 

Iceland tailors its escape routes and safety shelters (oftentimes schoolhouses, or reinforced community buildings) to adequately support the communities in the immediate surroundings of the natural hazard. In the case of the Bárðarbunga Caldera, the Vatnajökull glacier atop it creates the risk for dangerous flash flooding in the event the volcano wee to erupt. Levees have been placed around the town to mitigate this event to divert birth water and lava flow away from nearby communities.  Volcanologists monitor these natural hazards 24/7 and have the oublic practice evacuation routes. The public is also educated on the risks and dangers of these natural hazards. Measures are also being assessed to protect coastal towns from erosion (subsidence) and rising sea levels. The melting of the Vatnajökull glacier greatly contributes to this, as does global warming. Actions to be taken to mitigate these natural hazards are currently being assessed.



HOLUHRAUN LAVA FIELD The eruption in the central highlands began on August 31st 2014. Photo/Institute of Earth Sciences







Sources: http://icelandmag.visir.is/tags/subsidence

http://www.dailykos.com/story/2014/9/6/1327748/-B-r-arbunga-The-Greatest-Subsidence-Ever-Monitored-In-Iceland

Natural Hazards by Devecchio & Keller