Pleistocene volcanic debris avalanche from Mount Hagen, Papua New Guinea

Debris avalanches are rapid flowages of incoherent, unsorted mixtures of rock and soil material which move in response to gravity. On the southern and eastern slopes of Mt Hagen, a minimum area of 105 km²has been covered by chaotic deposits of matrix-supported clasts which form conical hills. The mean minimum thickness of the deposit is of the order of 30 m and the minimum volume is 3.2 km³. No source area for the avalanche can now be discerned on Mt Hagen but the headwaters area of the Gumants River seems the most likely. This absence of evidence of a source area and tephras overlying the deposit indicate that the debris avalanche occurred at least 80-100 ka and probably more than 400 ka. Emplacement of this avalanche may have contributed to the reversal of the Wahgi drainage.