No abstract

On palaeoclimate time scales, enhanced levels of geological and geomorphological activity have been linked to climatic factors, including examples of processes that are expected to be important in current and future anthropogenic climate change. Planetary warming leading to increased rainfall, ice-mass loss and rising sea levels is potentially relevant to geospheric responses in many geologically diverse regions. Anthropogenic climate change, therefore, has the potential to alter the risk of geological and geomorphological hazards through the twenty-first century and beyond. Here, we review climate change projections from both global and regional climate models in the context of geohazards. In assessing the potential for geospheric responses to climate change, it appears prudent to consider regional levels of warming of 2• C above average pre-industrial temperature as being potentially unavoidable as an influence on processes requiring a human adaptation response within this century. At the other end of the scale when considering changes that could be avoided by reduction of emissions, scenarios of unmitigated warming exceeding 4• C in the global average include much greater local warming in some regions. However, considerable further work is required to better understand the uncertainties associated with these projections, uncertainties inherent not only in the climate modelling but also in the linkages between climate change and geospheric responses.

Periods of exceptional climate change in Earth history are associated with a dynamic response from the geosphere, involving enhanced levels of potentially hazardous geological and geomorphological activity. The response is expressed through the adjustment, modulation or triggering of a broad range of surface and crustal phenomena, including volcanic and seismic activity, submarine and subaerial landslides, tsunamis and landslide 'splash' waves, glacial outburst and rock-dam failure floods, debris flows and gas-hydrate destabilization. In relation to anthropogenic climate change, modelling studies and projection of current trends point towards increased risk in relation to a spectrum of geological and geomorphological hazards in a warmer world, while observations suggest that the ongoing rise in global average temperatures may already be eliciting a hazardous response from the geosphere. Here, the potential influences of anthropogenic warming are reviewed in relation to an array of geological and geomorphological hazards across a range of environmental settings. A programme of focused research is advocated in order to: (i) understand better those mechanisms by which contemporary climate change may drive hazardous geological and geomorphological activity; (ii) delineate those parts of the world that are most susceptible; and (iii) provide a more robust appreciation of potential impacts for society and infrastructure.

In this study, we present evidence for early Holocene climatic conditions providing circumstances favourable to major lateral collapse at Mount Etna, Sicily. The volcano's most notable topographic feature is the Valle del Bove, a 5 × 8 km cliff-bounded amphitheatre excavated from the eastern flank of the volcano. Its origin due to prehistoric lateral collapse is corroborated by stürtzstrom deposits adjacent to the amphitheatre's downslope outlet, but the age, nature and cause of amphitheatre excavation remain matters for debate. Cosmogenic 3 He exposure ages determined for eroded surfaces within an abandoned watershed flanking the Valle del Bove support channel abandonment ca 7.5 ka BP, as a consequence of its excavation in a catastrophic collapse event. Watershed development was largely dictated by pluvial conditions during the early Holocene, which are also implicated in slope failure. A viable trigger is magma emplacement into rift zones in the eastern flank of a water-saturated edifice, leading to the development of excess pore pressures, consequent reduction in sliding resistance, detachment and collapse. Such a mechanism is presented as one potential driver of future lateral collapse in volcanic landscapes forecast to experience increased precipitation or melting of ice cover as a consequence of anthropogenic warming.

We present statistical evidence for a temporal link between variations in the El Niño-Southern Oscillation (ENSO) and the occurrence of earthquakes on the East Pacific Rise (EPR). We adopt a zero-inflated Poisson regression model to represent the relationship between the number of earthquakes in the Easter microplate on the EPR and ENSO (expressed using the southern oscillation index (SOI) for east Pacific sea-level pressure anomalies) from February 1973 to February 2009. We also examine the relationship between the numbers of earthquakes and sea levels, as retrieved by Topex/Poseidon from October 1992 to July 2002. We observe a significant (95% confidence level) positive influence of SOI on seismicity: positive SOI values trigger more earthquakes over the following 2 to 6 months than negative SOI values. There is a significant negative influence of absolute sea levels on seismicity (at 6 months lag). We propose that increased seismicity is associated with ENSO-driven sea-surface gradients (rising from east to west) in the equatorial Pacific, leading to a reduction in ocean-bottom pressure over the EPR by a few kilopascal. This relationship is opposite to reservoirtriggered seismicity and suggests that EPR fault activity may be triggered by plate flexure associated with the reduced pressure.