Page 19 - Spring 2018
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 Robin S. Matoza
Department of Earth Science and Earth Research Institute University of California, Santa Barbara Santa Barbara, California 93106-9630 USA
David Fee
Wilson Alaska Technical Center Alaska Volcano Observatory Geophysical Institute University of Alaska, Fairbanks Fairbanks, Alaska 99775-7320 USA
The Inaudible Rumble of Volcanic Eruptions
Volcanic eruptions produce powerful infrasound that can be used to moni- tor and mitigate volcanic hazards.
Introduction and Context
There are approximately 1,500 volcanoes worldwide that are considered potentially active, defined as a volcano at which an eruption has occurred within the past 10,000 years (Global Volcanism Program, 2013; Figure 1). Eruptions are common; for example, more than 50 eruptions have occurred in the United States in the past 31 years (National Academies of Sciences, Engineering, and Medicine, 2017). Approximately 500 million people worldwide are directly exposed to volcanic haz- ards. This number is steadily increasing as population density grows in areas near volcanoes. Fortunately, many eruptions are preceded by unrest, and volcano-mon- itoring scientists use an array of different ground-based, airborne, and spaceborne techniques to detect this unrest, track eruption progression, build understanding of how volcanoes work, and provide timely warnings where possible. However, many potentially active volcanoes are located in remote and inhospitable regions of the planet where it is challenging to install and maintain dedicated local moni- toring instruments. Although such volcanoes may be located in sparsely populated areas, explosive eruptions at these remote volcanoes can inject large volumes of ash into heavily traveled aviation routes, posing a major societal and economic hazard (Casadevall, 1994). Volcanic ash consists of tiny particles (<2-mm grain size) of solid rock, with a melting temperature below the operating temperature of jet engines. Encounters between volcanic ash and aircraft have resulted in engine
Figure 1.Global potentially active volcanoes (eruption in past 10,000 years; red triangles), tectonic plate boundaries (black lines: solid, ridge plate boundary type; dashed, trench plate boundary type; dotted, transform plate boundary type), and the planned 59-station Interna- tional Monitoring System (IMS) infrasound network (open inverted triangles). At present, 49 stations are operational. Each infrasound station consists of a small array of infrasonic sensors deployed in a variety of spatial configurations with maximum dimensions of 1-2 km across the ground surface. The average station spacing for the complete network will be about 2,000 km. Modified from Matoza et al. (2017), with permission.
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