HOLOCENE JÖKULHLAUPS, NORTH WESTERN MÝRDALSJÖKULL, ICELAND – NEW EVIDENCE AND WIDER SIGNIFICANCE

This poster presents new evidence for prehistoric jökulhlaup activity from the north western sector of Mýrdalsjökull ice cap, Iceland.

Mýrdalsjökull lies over the highly active Katla caldera. Two main types of activity are characteristic of Katla – silicic and basaltic eruptions. The basaltic activity is associated with large-scale flooding. No floods from silicic eruptions have yet been identified, but widespread ocean-transported silicic pumice from Katla has been found on coasts around the North Atlantic. This pumice most probably reached the sea via jökulhlaups. The next Katla eruption is now overdue.

Historic flood activity to the east and prehistoric floods to the south of the ice cap have been well constrained from historical and geomorphological studies. However, little has been documented about flood activity to the north west of the ice cap.

I have identified and dated 4 main units that may be associated with prehistoric flood activity in this critical north western sector of the ice cap. One lithic rich diamicton, similar to documented hyperconcentrated flow deposits, occurs in numerous sections. A further three pumice-rich units with crude bedding and few structures show similarities to flood deposits on the south coast of Iceland. Extensive erosional and depositional landforms characteristic of high magnitude floods have been identified throughout this region. No historical jökulhlaup deposits have been recorded.

These findings are important because they indicate that west of the ice cap has been, and may again be, an active jökulhlaup route with associated hazard implications. Also, they confirm that flood routes from Katla have changed through time. This may be associated with changing configurations of the ice cap or changing locations of volcanic activity. As yet no terrestrial evidence has been found for silicic jökulhlaups. Continuation of this study will assess whether major floods are associated with silicic Katla eruptions and examine likely flood routes.