Guillas et al. note that this provides an example of how variations in the atmosphere and hydrosphere can drive very small changes in environmental conditions that are able, in turn, to trigger a response from the Earth’s crust. Most importantly, they speculate that, in a warmer world, comparable and larger changes associated with ocean loading due to global sea level rise, or unloading associated with the passage of more intense storms, may trigger more significant earthquake activity at submarine fault systems that are in a critical state.
Continuing the theme, Hampel et al. take a broader look at how faults have responded to variations in ice and water volumes as a consequence of past climate change. Using numerical models, the authors demonstrate that climate-driven changes in ice and water volume are able to affect the slip evolution of both thrust and normal faults, with—in general—both the slip rate and the seismicity of a fault increasing with unloading and decreasing with loading. Adopting a case-study approach, Hampel and colleagues provide evidence for a widespread, post-glacial, seismic response on faults located beneath decaying ice sheets or glacial lakes. Looking ahead, the authors point to the implications of their results for ice-mass loss at high latitudes, and speculate that shrinkage of the Greenland and Antarctic ice sheets as a consequence of anthropogenic warming could result in a rise in the frequency of earthquakes in these regions.
In a similar vein, Sigmundsson et al. evaluate the influence of climate-driven ice loading and unloading on volcanism, focusing on Iceland and, in particular, on the Vatnajökull ice cap. Noting that a significant pulse of volcanism in Iceland, at the end of the last glaciation, flags a link between unloading and volcanism, the authors model the effects of contemporary ice-mass loss at Vatnajökull on future magmatic activity. Using a viscoelastic model of glacio-isostatic adjustment that incorporates melt generation in the underlying mantle, Sigmundsson and co-authors predict that ice wastage will result in additional magma generation beneath Iceland. The authors expect more frequent or more voluminous volcanic activity to be a consequence of enhanced melt generation, but also observe that it could take longer than decades or centuries for the resulting magma to reach the surface. Sigmundsson et al. also show that ice unloading is likely to drive shallow magma reservoirs progressively towards failure, although this effect will be small and therefore contribute only to modulating ‘normal’ activity.
A more general evaluation of the impact of a changing climate on glaciated volcanoes is undertaken by Tuffen, who looks ahead to how the melting of ice caps on active volcanoes may influence volcanic hazards in the 21st century. In reviewing the evidence for current melting of ice increasing the frequency or size of future eruptions, Tuffen notes that much remains to be understood in relation to ice loss and increased eruptive activity. In particular, uncertainty surrounds the sensitivity of volcanoes to small changes in ice thickness and how rapidly volcanic systems respond to deglaciation. Nonetheless, Tuffen expects an increase in explosive eruptions at glaciated volcanoes that experience significant ice thinning, and increased frequency of lateral collapse at glaciated strato-volcanoes in response to anthropogenic warming.
On the positive side, deglaciation may ultimately reduce the threat from volcanic debris flows (lahars) and meltwater floods from volcanoes that currently support ice caps.
Volcano lateral collapse in response to a changing climate is explored further in the final research paper by Deeming et al., although in this case the driving force is precipitation rather than ice-mass loss. Deeming and co-workers present the results of a cosmic-ray exposure dating campaign at Mount Etna (Sicily), which constrains the timing and nature of collapse of the Valle del Bove, a major volcanic landslide scar on the eastern flank of the volcano. The authors link pluvial conditions during the early Holocene to the formation of a high-energy surface drainage system and to its truncation by a catastrophic lateral collapse event, ca7.5 ka BP, which opened the Valle del Bove. A possible mechanism is proposed, whereby magma emplacement into a water-saturated edifice caused the thermal pressurization of pore water, leading to a reduction in sliding resistance and subsequent large-scale slope failure. Deeming et al. present the mechanism as one possible driver of future lateral collapse at ice-capped volcanoes and at those located in regions predicted to experience enhanced precipitation.
Concluding the volcanoes and climate change theme, Tuffen and Betts draw together the thoughts of delegates at a second colloquium discussion session, which focused on Volcanism and climate: chicken and egg (or vice versa )? Among other outcomes of the discussion came the feeling that the title of the session was too prescriptive, with perhaps ‘Chicken and egg’ being more appropriate. This, it was broadly felt, better reflected the complexities apparent in the volcano–climate system, within which both climate forcing of volcanism and volcanic forcing of climate appear to play a part. Going further, rather than a chicken and egg debate, it was suggested that it might be more beneficial to concentrate efforts on understanding better how the volcano–climate system evolves over time, responds to different forcings, and incorporates various feedback mechanisms. Among other proposals, it was advocated that climate models should incorporate variable volcanic inputs so as to better explore how volcanic activity might affect the climate in the future.
Together, this set of papers provides a coherent whole that addresses a wide range of issues relating to how climate change may force geological and geomorphological phenomena capable of acting to increase natural hazard risk in a warmer world. They reflect a field of research that is only now becoming recognized as important in the context of the likely impacts and implications of anthropogenic climate change. We hope that this Theme Issue will provide a marker that reinforces the idea that anthropogenic climate change does not simply involve the atmosphere and hydrosphere, but can also elicit a response from the Earth’s crust and mantle. In this regard, we hope that it will encourage further research into those mechanisms by which climate change may drive potentially hazardous geological and geomorphological activity, and into the future ramifications for society and the economy.