Paleohydrology of Volcanogenic Lake Break-Out Floods in the Taupo Volcanic Zone, New Zealand

Abstract

Volcanically active regions, like the Taupo Volcanic Zone (TVZ) in the central North Island of New Zealand, are an ideal environment for the temporary impoundment of surface water because of the basin-forming properties of explosive eruptions and volcano-tectonic faulting, and the valley-damming potential of pyroclastic and lava flows, lahar deposits, and debris avalanches. Historic break-out floods are known from two lakes, the summit Crater Lake of Mt. Ruapehu, and intra-caldera Lake Tarawera, but careful analysis of the geologic record shows abundant evidence for older floods on much larger scales in other settings. The largest flood so far recognised involved the release of c. 60 km3 of water from intracaldera Lake Taupo following a caldera-forming eruption at 26.5 ka: the recurrent nature of such hazards is shown by a similar 20 km3 break-out in the aftermath of the 1.8 ka Taupo eruption. Multiple prehistoric paleofloods are recognised or inferred at several other volcano-lake centres. Paleohydraulic analyses of these events show that in terms of volume and peak discharge they are amongst the largest known late Pleistocene floods worldwide, only being exceeded by break-outs from pro-glacial lakes impounded by continental ice-sheets, overspilling of pluvial lakes in tectonic basins, or some Icelandic jokulhlaups.