Climate Extremes

Earthquakes

Floods

Climate Change

Volcanoes

Tsunamis
Indian Ocean Tsunami

Landslides

Disaster Studies & Management
Rapid Environmental Impact Assessment in Disaster Response


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Recently completed PhDs

Patrick Erwin

Volcanic eruptions producing pyroclastic flows and volcano sector collapses producing debris avalanches are potentially some of the most hazardous geological processes. Our understanding of the fluid dynamics of pyroclastic flows and volcanic debris flows, and our knowledge of the processes by which volcanoes become unstable, is limited. One technique, which has been used to gain insights into these processes, is the derivation of the emplacement temperature of debris-avalanche and pyroclastic flow deposits. Of the various methods available, only the palaeomagnetic technique is generally applicable. However, this technique has never before been tested in a geological environment.

In this thesis, the palaeomagnetic technique of estimating emplacement-temperatures is tested by analysis of the 1980 deposits of Mount St. Helens, where both the emplacement temperatures and the cooling rates are well constrained. This is the first attempt at validating the technique in a geological environment.

Without corrections, the technique is shown to work semi-quantitatively. Existing theoretical methods of correction (Dodson & McClelland Brown, 1980) are applied to the data and shown to dramatically improve the correlation. These are then developed to account for the magnetic mineralogies commonly found in volcaniclastic rocks (e.g. Mount St. Helens). The technique is shown, at least in this test case, to yield estimates which are at most 5°C in variance with the real emplacement temperature.

The technique in its semi-quantitative form is applied to a series of volcano collapse deposits, the Murimotu Formation, on Ruapehu, New Zealand, the Ayacata Formation, Gran Canaria, and an aborted volcano collapse structure, the San Andrés Fault, El Hierro. These edifices were generally not at elevated temperatures immediately before collapse; however, the Murimotu formation exhibits a localized hotspot in its core.

These data are consistent with recent work highlighting the importance of hydrothermal pressurization as a mechanism of inducing volcano instability.