If you ever frequent Jon Frímann's blog, you know that he tends to find all the news about potential Icelandic rumblings before pretty much everyone. Well, he seems to have found something interesting going on up in Iceland - a few news reports (in Icelandic) have been talking about the crater lake on Askja caldera having mysteriously become ice-free over the last month while lakes around it (that aren't on volcanoes) and at lower elevations are still ice-covered - not to mention that normally the lake isn't ice-free until June or July. This has lead to a lot of speculation about what exactly is going on at Askja, but thanks to its remote location almost in the middle of Iceland, few people have been out there to see what is going on.
A little background on the volcano. Askja is a very complex volcano made up of three calderas. The volcano has mostly erupted basaltic material over its recent history, but it has also had a rhyolitic eruption over 10,000 years ago. Now, usually at a basaltic volcano, the calderas are formed by passive sinking of the land surface, much like we see in Hawai'i. However, at Askja, it appears that the calderas are formed more violently due to explosive eruptions out of the ring fractures bounding the calderas. The youngest caldera formed only 137 years ago (in 1875) and the ~4.5 km diameter feature is home to two crater lakes, Öskjuvatn and Víti. The former is the larger lake, over 200 meters deep, while the latter is a very small, warm crater lake (marked in the photo above near the word "ash?").
The most recent activity at Askja was in 1961 that produced lava flows near Öskjuvatn - a pattern of eruption that was seen in numerous times since the VEI 5 eruption in 1875. That caldera-forming eruption in 1875 was large enough that ash and tephra fell as far away as Norway and Sweden. Much like the 2010 Eyjafjallajökull eruption, the explosivity of the eruption was likely aided by the meltwater that is readily available at Askja. If you go back to the rhyolite eruption in ~8910 B.C., that ash from that caldera-forming event is found over much of Europe.
After hearing about the melting ice on Askja, I asked Robert Simmon from the NASA Earth Observatory is they had any imagery of the Askja are to see if I could see the melting for myself. Well, as you might guess, trying to image the middle of Iceland in winter from space is, ahem, problematic. However, Robert did find three image that show the lake becoming more-and-more ice-free between February 23 and March 23. The most recent image is at the top and shows Öskjuvatn nearly ice-free. It also shows Víti on the top right of Öskjuvatn and a coating of something on the snow surrounding Víti. {SPECULATION ALERT} Now, it is marked as ash on the image, but there is no confirmation. However, it is hard to come up with any other explanation - some idea might be windblown dust from inside the small warm crater lake or staining from fumaroles that can occur inside Víti. If it were ash, it could be from steam explosions inside Víti that blasted little material out as the water got hot enough to form steam. This discoloration is not visible on the March 6 image (see below), so something new has happened {SPECULATION END}.
In the sequence of three images I tried to mark at least one feature that can be seen in all the images as a reference, but it does seem that the ice had melted on the western side of the lake (starting before February 26) and progressed eastward across Öskjuvatn. Now, why is it melting? What I've read suggests that it could be volcanic or meteorologic. The volcano rationale is easy - hot springs and fumaroles at the bottom of the lake are heating the water, causing the ice to melt. The meteorologic involves specific wind patterns that have happened this winter, along with the abnormally warm winter in Iceland. I'm not going to say that either has to be the answer, however, seismicity around Askja has been increasing over the last few years, suggesting magma rising under the volcano, but right now, seismicity is relatively quiet.
Scientists from the Icelandic Meteorological Office and the University of Iceland will be trekking to Askja (Icelandic) this weekend to take measurements and set up instruments to help solve this mystery of the melting ice. In the meantime, the Icelandic government has declared the volcano "off-limits" to tourists on concerns of "the possibility of toxic gases". Until we have more information, we can only guess what might be going on at Askja right now.
Image 1: Askja crater lake March 23, 2012. NASA/USGS EO-1 ALI. Courtesy of the NASA Earth Observatory.
Image 2: Askja crater lake February 26, 2012, NASA/USGS ALI E0-1 panchromatic. Courtesy of the NASA Earth Observatory.
Image 3: Askja crater lake March 5, 2012, NASA/USGS EO-1 ALI panchromatic. Courtesy of the NASA Earth Observatory.
Special thanks to Robert Simmon (images) and Jon Frimann (links) used in this post.
