| Summary: | In this study the buried edge of the Álftaver lava flow below Mýrdalssandur is located with magnetic measurements. The Álftaver lava flow was produced in the Eldgjá eruption 934 AD, which is one of the largest flood lava eruptions in the last 1100 years. The lava flow was formed in several eruptive events during a 3-8 year period. Most recent volume estimates put it at ~18 km3. The lava followed rivers and gorges down to the lowlands of Álftaver, Landbrot and Meðalland and formed large lava fields called the Eldgjá lava flow. The lava fields raised the topography, dammed rivers and altered their flow pattern. Since the eruption sediments have accumulated at Mýrdalssandur from jökulhlaups coming from beneath the Kötlujökull glacier. At first the Álftaver lava was a barrier for jökulhlaups from flowing across it to the east. However, Mýrdalssandur built up quickly until the floods were able to flow over the Álftaver lava flow. Thus, a part of the lava flow is now buried beneath Mýrdalssandur. In total 14 magnetic profiles were measured with a proton magnetometer and GPS. The total length of the profiles measured is ~75 km. The measurements were conducted across previously determined, 1-15 km long profiles, lying approximately perpendicular to the edge of the lava flow. The measurements were for the most part performed on foot and partly by car. Measurements were done at 2 sec intervals where the total magnetic field in nT and the GPS position was measured. The principle aim of the survey was identifying changes in depth to magnetic sources. Segments of individual profiles with similar spacing of anomalies (spatial frequency) and anomaly amplitudes were identified visually on the profiles. Changes in spatial frequency were used to identify the location of the buried lava edge as well as lava ledges. Maximum depth to magnetic sources was estimated with the Peters half slope method. The measurements revealed the edge further to the west than previously assumed. The lava edge was found ~5 km east of Hafursey and ~8 km ...
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