Dike Propagation Models of Tiltmeter Data from the 1984 Rifting Event at Krafla Volcano, Iceland

The dynamics of magma transport within sections of the mid-ocean ridge are not well known. Although opportunities for direct observation of magma transport are rare, many studies have been made on subaerial regions of the mid-ocean ridges (e.g., Iceland) and on ophiolites to try to understand the processes of crustal accretion and dike intrusion along spreading ridges. As a first step, resolving the directions and rates of dike propagation is critical for determining the appropriate thermodynamics and fluid mechanics of dike intrusions within mid-ocean ridges. The most recent eruption of Krafla volcano in northeast Iceland provides an opportunity for resolving the direction and rates of dike propagation with geodetic data. The September 1984 Krafla eruption occurred within a network of continuously recording tiltmeters [Tryggvason, 1986]. We present models of the Krafla tiltmeter record because of its importance for studies of midocean ridge magma transport and because there is currently a controversy between the direction of dike propagation inferred from seismicity and petrology. While the seismic data from the Krafla eruptions are consistent with lateral dike propagation (away from the deflating magma chamber) [Einarsson and Brandsdottir, 1980], the geochemical and petrological data are better explained by vertical magma transport. Therefore, we have begun to analyze a third data set, the continuous tiltmeter record, to estimate the direction of dike propagation. The prior analysis of Arnadottir et al. [1998] allows us to focus our modeling efforts on the dike propagation. Preliminary results favor a vertically propagating dike. The east component of tilt recorded at Litli Leirhnj—kur, a station that is ~0.75 km from the dike, reverses its sign during the dike propagation, which is consistent with a vertically propagating dike. Data from the other two stations, Krafla and Viti (located ~2 km from the southern end of the dike), will be used to help constrain the time history, direction of dike growth, and magma chamber deflation.