"By the end of May, the land level over the magma reservoirs at Krafla had regained the height reached prior to the 16 March deflation and eruption. A new event was therefore expected as tiltmeters showed continuous height increase indicating further magma inflow into the reservoirs.

"On 10 July at about 0800, the continuously recording tiltmeters started to show rapid deflation and about 1 hour later volcanic tremor was noted on the seismometers. Earthquake activity was soon seen to migrate northwards along the Krafla fault swarm. At about 1245 an eruption started about 8 km N of the magma reservoirs. At least four groups of fissures were active extending over about 4 km. Activity was greatest during the first day but then decreased and concentrated in the northernmost crater group. The eruption then continued with decreasing vigor until 18 July when activity faded away in the early morning.

"The eruption took place far away from habitation so damage was minimal. The beginning of the eruption was observed from the air and on the ground by an unsuspecting tourist.

"The eruption was accompanied by large-scale fault movements close to the eruption site. Possibly the most spectacular sight was when large volumes of lava disappeared down into one of the faults about 3 km from the crater. This lasted for a few hours and the width of the falls was about 200 m.

"The lava covers 5-6 km² and is much thicker than in previous eruptions. Preliminary volume estimates indicate that the volume of erupted lava exceeds that which left the central magma reservoirs. This is the first time during the Krafla rifting episode when no magma appears to have been added to the rift zone.

"Inflation of the magma reservoirs started again on 16 July, before the eruption was over. Inflation now continues at a high rate so that the Krafla rifting and magmatic episode continues."

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.