A slope at Barry Arm, in Alaska’s Prince William Sound, is deforming at a varying rate up to tens of meters per year above a retreating glacier and deep fjord that is a popular recreational destination. If the estimated 500 million cubic meters of unstable material on this slope were to fail catastrophically, the impact of the landslide with the ocean would produce a tsunami that would not only endanger those in its immediate vicinity, but likely also those in more distant areas such as the port of Whittier, 50 km away. The discovery of this threat was happenstance, and the response so far has been cobbled together from over a dozen existing grants and programs. Remotely sensed imagery could have revealed this hazard a decade ago, but nobody was looking, highlighting our lack of coordination and preparedness for this growing hazard driven by climate change. As glaciers retreat, they can simultaneously destabilize mountain slopes and expose deep waters below, creating the potential for destructive tsunamis. The settings where this risk might occur are easily identified, but more difficult to assess and monitor. Unlike for volcanoes, active faults, landslides, and tectonic tsunamis, the US has conducted no systematic assessment of tsunamis generated by subaerial landslides, nor has the US established methods for monitoring or issuing warnings for such tsunamis. The U.S. National Tsunami Warning Center relies on seismic signals and sea-level measurements to issue warnings; however, landslides are more difficult to detect than earthquakes, and the resultant tsunamis often would reach vulnerable populations and infrastructure before water level gages could help estimate the magnitude of the tsunami. Also, integrating precursory motion and other clues of an impending slope failure into a tsunami warning system has only been done outside the US (e.g Norway: Blikra et al., 2012). Barry Arm is a dramatic case study highlighting these challenges and may provide a model for mitigating the threat of tsunamis generated by subaerial landslides enabled by glacial retreat elsewhere.

Prolonged volcanic activity can induce surface weathering and hydrothermal alteration that is a primary control on edifice instability, posing a complex hazard with its challenges to accurately forecast and mitigate. This study uses a frequently active composite volcano, Mt Ruapehu, New Zealand, to develop a conceptual model of surface weathering and hydrothermal alteration applicable to long-lived composite volcanoes. The rock samples were classified as non-altered, supergene argillic alteration, intermediate argillic alteration, and advanced argillic alteration. The first two classes have a paragenesis that is consistent with surficial infiltration and circulation of the low-temperature (40 degree C) neutral to mildly acidic fluids, inducing chemical weathering and formation of weathering rims on rock surfaces. The intermediate and advanced argillic alterations are formed from hotter (100 degree C) hydrothermal fluids with lower pH, interacting with the andesitic to dacitic host rocks. The distribution of weathering and hydrothermal alteration has been mapped with airborne hyperspectral imaging through image classification, while aeromagnetic data inversion was used to map alteration to several hundred meters depth. The joint use of hyperspectral imaging complements the geophysical methods since it can numerically identify hydrothermal alteration style. This study established a conceptual model of hydrothermal alteration history of Mt Ruapehu, exemplifying a long-lived and nested active and ancient hydrothermal system. This study highlights the need to combine mineralogical information, geophysical techniques and remote sensing to distinguish between current and ancient hydrothermal and supergene alteration systems, to indicate the most likely areas of future debris avalanche initiation.