"The relatively slow but steady inflation of Krafla was interrupted by a minor deflation event 3-10 December. This deflation was very slow and no volcanic tremor was observed. Inflation resumed on 10 December and on 15 December the previous ground level had been reached.

"The number of earthquakes in the vicinity of the magma chambers had increased gradually in November, but during the mini-deflation earthquake activity decreased to background levels. When the previous ground level was exceeded in the second half of December, the number of recorded earthquakes started to increase again. The largest, of estimated magnitude 4, took place on 3 January and was widely felt in the area."

Geological Summary. The Krafla central volcano, located NE of Myvatn lake, is a topographically indistinct 10-km-wide caldera that is cut by a N-S-trending fissure system. Eruption of a rhyolitic welded tuff about 100,000 years ago was associated with formation of the caldera. Krafla has been the source of many rifting and eruptive events during the Holocene, including two in historical time, during 1724-29 and 1975-84. The prominent Hverfjall and Ludent tuff rings east of Myvatn were erupted along the 100-km-long fissure system, which extends as far as the north coast of Iceland. Iceland's renowned Myvatn lake formed during the eruption of the older Laxarhraun lava flow from the Ketildyngja shield volcano of the Fremrinamur volcanic system about 3800 years before present (BP); its present shape is constrained by the roughly 2000 years BP younger Laxarhraun lava flow from the Krafla volcanic system. The abundant pseudocraters that form a prominent part of the Myvatn landscape were created when the younger Laxarhraun lava flow entered the lake.

Information Contacts: K. Grönvold, NVI.