Summit acid crater lakes and flank instability in composite volcanoes

Volcanic landslides, including flank and sector collapses, constitute a major hazard in many parts of the world. While composite volcanoes are innately unstable, the presence of a hydrothermal system maintained by a magmatic source at depth is recognized as a key factor increasing the risk of failure. This relates to the formation of hydrothermally altered rock masses within the core and upper flanks of the volcano which leads to heterogeneous distribution of rock strength properties and pore fluid pressures. Here an emphasis is placed on acid crater lakes perched high on active volcanoes. By acting as a trap for magmatic heat and gas flows, these lakes localize extreme acid attack on their surrounds, thereby creating a source of instability. We outline how acid crater lakes form in relation to magmatic hydrothermal systems hosted within composite volcanoes, and describe the associated hydrothermal alteration and its relationships to flank instability. The sustainability of a volcanic slope is partly governed by the degree of rock alteration, which in turn reflects the time-integrated flux of acidic gases (SO2 and HCl) released from the subsurface magmatic source. Transient or longer-term changes in pore fluid pressure linked to hydrothermal system activity also readily affect the slope stability of composite volcanoes. Such fluctuations can be initiated by both magmatic and external non-magmatic processes such as major rainfall events and regional seismicity. Kawah Ijen hyper-acid crater lake, Indonesia, is used as a case study to illustrate the cascade of effects that may ensue following slope rupture linked to hydrothermal alteration

Radiative forcing and climate impact resulting from SO2 injections based on a 200,000 year record of Plinian eruptions along the Central American Volcanic Arc

We present for the first time a self-consistent methodology connecting volcanological field data to global climate model estimates for a regional time series of explosive volcanic events. Using the petrologic method, we estimated SO2 emissions from 36 detected Plinian volcanic eruptions occurring at the Central American Volcanic Arc (CAVA) during the past 200,000 years. Together with simple parametrized relationships collected from past studies, we derive estimates of global maximum volcanic aerosol optical depth (AOD) and radiative forcing (RF) describing the effect of each eruption on radiation reaching the Earth’s surface. In parallel, AOD and RF time series for selected CAVA eruptions are simulated with the global aerosol model MAECHAM5-HAM, which shows a relationship between stratospheric SO2 injection and maximum global mean AOD that is linear for smaller volcanic eruptions (<5 Mt SO2) and nonlinear for larger ones (≥5 Mt SO2) and is qualitatively and quantitatively consistent with the relationship used in the simple parametrized approximation. Potential climate impacts of the selected CAVA eruptions are estimated using an earth system model of intermediate complexity by RF time series derived by (1) directly from the global aerosol model and (2) from the simple parametrized approximation assuming a 12-month exponential decay of global AOD. We find that while the maximum AOD and RF values are consistent between the two methods, their temporal evolutions are significantly different. As a result, simulated global maximum temperature anomalies and the duration of the temperature response depend on which RF time series is used, varying between 2 and 3 K and 60 and 90 years for the largest eruption of the CAVA dataset. Comparing the recurrence time of eruptions, based on the CAVA dataset, with the duration of climate impacts, based on the model results, we conclude that cumulative impacts due to successive eruptions are unlikely. The methodology and results presented here can be used to calculate approximate volcanic forcings and potential climate impacts from sulfur emissions, sulfate aerosol or AOD data for any eruption that injects sulfur into the tropical stratosphere