THE OBSERVED ROLE OF EXTERNAL WATER IN LARGE ALEUTIAN ARC ERUPTIONS

Nearly every volcano in the Aleutian arc has some amount of permanent ice and snow cover, and many volcanic edifices support ice volumes in excess of 5 km³. More than a few volcanoes in the Aleutian arc also have summit crater lakes and robust hydrothermal systems associated with poorly understood edifice-scale groundwater flow systems. Regardless of its physical state, external water on volcanoes is an important factor in the scale, style, and outcome of explosive eruptive activity and is a key variable influencing the types of eruptive products generated and the degree of hazard associated with them. Thus, an improved understanding of the role of external water during eruptions serves as a potentially useful framework for evaluating unrest likely to culminate in eruption, the interpretation of eruptive products, and the forecasting hazards associated with excess water on volcanoes.

To illustrate the concepts of external water-volcano interactions, several historical Aleutian arc eruptions are reviewed, including the 2008 eruption of Kasatochi volcano, the 2009 eruption of Redoubt Volcano, the Pavlof eruptions of 1996, 2007, 2013 and 2014, and the Holocene caldera-forming eruptions of Veniaminof Volcano. In each case, the role of external water during eruptive activity is evaluated from the perspective of both field and remote observations. Examples presented show that the interactive processes among eruptive products and snow, ice, and water depend on the style of eruption and the specific types of eruptive products generated. In some cases, the course of the eruption and resulting hazards are directly related to the effects of ice and snow.