"The early phase of the September eruption (9:8) was very similar to previous eruptions. Maximum eruptive activity was reached within about 1 hour, and while the whole 8.5-km-long fissure was active thin fluid lava advanced along the entire zone (figure 8). In the early hours of the eruption's first morning, 5 September, activity decreased rapidly, dying out on many of the fissure segments, especially in the southern half. By 6 September only one crater remained active, just S of the N end of the original fissure.

Figure 8. Sketch map of the Krafla area by Kristjan Saemundsson (NVI) made with the aid of airphotos by Oddur Sigurdsson at the same institute. Lava flows from the September 1984 eruption are shown in a stipple pattern. Courtesy of Karl Grönvold.

"By midday 5 September, while activity was dying out along most of the fissure, deflation over the magma reservoirs below Leirhnjúkur stopped and inflation began (figure 9). This situation changed on 9 September when deflation resumed. Around the same time, activity at the one remaining crater increased. Deflation and relatively vigorous eruption continued until the afternoon of 18 September when activity at the crater died out and inflation resumed. The inflation pattern since then is similar to that following previous eruptions.

Figure 9. Tilt at the Krafla powerhouse (Kröfluvirkjun), top, and Víti (~3 km NE of the powerhouse), bottom, 4-27 September 1984. Vertical lines are time signals at midnight. Courtesy of Gudmundur Sigvaldason.

"The new lava covers about 24 km² and the total area now covered by Krafla lava is about 36 km². As in some of the previous eruptions lava was observed flowing into older fissures, causing secondary rifting. Sometimes this lava reemerged farther along the fissures. Flames from burning gas were widely observed near the flow margin."

Further Reference. Tryggvason, E., 1986, Multiple magma reservoirs in a rift zone volcano: ground deformation and magma transport during the September 1984 eruption of Krafla, Iceland: JVGR, v. 28, p. 1-44.

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 and G. Sigvaldason, NVI; P. Einarsson, Univ. of Iceland.