"After a quiet interval of 2 years and 9 months, an eruption broke out at Krafla on 4 September 1984. The eruption in November 1981 (6:11) and associated deflation of magma reservoirs below Leirhnjúkur were followed by inflation, reaching previous levels in early 1982. Since then slow and intermittent inflation has continued, accompanied by earthquakes in the reservoir roof.

"Rapid deflation over the magma reservoirs followed by volcanic tremor began 4 September at about 2025, but the eruption broke out at 2349. The beginning of the eruption was observed from the air by alerted scientists and a television reporter. The first fissure segment opened about 6 km N of Leirhnjúkur, followed within a minute by another about 3 km to the S. The fissures quickly joined and in 1 hour reached their full length of 8.5 km, extending from Leirhnjúkur to the N. During the first hours lava was erupted along the whole fissure, advancing on broad fronts.

"Already in the early hours of the morning, the activity had decreased and lava production on various sections of the fissures had faded out. By midday on 5 September, inflation had resumed. By 6 September, eruption on the S part of the fissure had ceased except on one crater, which then changed into phreatic activity.

"By 8 September, inflation rates over the magma chambers diminished and slow deflation started [but see 9:11]. On the northernmost part of the fissure, activity continued as of the morning of 12 September with significant lava production.

"As in previous eruptions, lava production was highest on the northern part of the fissure and has so far not constituted any threat to inhabited areas."

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; P. Einarsson, Univ. of Iceland.