Mount Redoubt in action. Credit: G. McGimsey/Alaska Volcano Observatory/USGS

The eruptions of Llaima in central Chile, which began on 3 April, and of Mount Redoubt in Alaska, which has been rumbling on since 22 March, have provided new impetus for volcano monitoring systems.

In the United States, politicians have been galvanized by the eruption of Mount Redoubt, about 180 kilometres southwest of Anchorage. On 2 April Senator Lisa Murkowski (Republican, Alaska) introduced legislation to provide the US Geological Survey (USGS) with US$15 million a year for an expanded nationwide network of monitoring instruments.

At the same time, US geologists are travelling to Chile to help that country wire up its volcanoes. Llaima, which erupts frequently, is one of only a handful of Chile's 122 active volcanoes currently monitored.

The 2 May 2008 eruption of the Chaitén volcano drew attention to the unmonitored majority. The eruption forced the evacuation of the 4,000 residents of the nearby town of Chaitén, rendered it uninhabitable and disrupted air traffic for months. In its aftermath, Chilean President Michelle Bachelet decided to try and fund monitoring for 40 of the country's most dangerous volcanoes over the next 5 years.

Chilean volcanologists hope to spend US$4 million installing equipment on eight high-priority volcanoes in the coming year. Hardware for the new system has been ordered and is expected to arrive in June, says Luis Lara of Chile's National Geology and Mineral Service. In January, USGS scientists from the Cascades Volcano Observatory in Vancouver, Washington, spent three weeks helping their Chilean counterparts to organize the system. The same USGS team returned last week from Indonesia, where it has been helping scientists install seismometers on volcanoes on Sulawesi. The USGS has also collaborated with Colombia in the past two years on early detection of eruptions.

The United States and its territories contain 169 volcanoes that are geologically active, but at present only about half of the most threatening volcanoes have basic seismic arrays. In 2005, the USGS proposed a National Volcano Early Warning System to expand instrumentation, but without backing by Congress or the president the plan was shelved. The highest priority volcanoes listed were five that were actively erupting or "showing periods of significant unrest" in 2005, including Mount St Helens in Washington and Kīlauea in Hawaii; 13 "very high threat" volcanoes — four in Alaska and nine in the Cascade Range in the western United States; and 19 volcanoes in Alaska and the Mariana Islands that threaten aviation routes but have no real-time, ground-based monitoring to pick up precursors to eruptions.

Cracking the problem

Mount Redoubt shows the benefits of monitoring, which in its case began after undetected eruptions nearly brought down an aircraft by clogging its jet engines in the 1980s. Last October, spectrometry equipment at the site detected increased sulphur-dioxide emissions, prompting the USGS to fly regular gas-checking flights. Then in the days before the first eruption, seismometers provided the needed alert. A coastal oil-drilling facility was evacuated, and international aircraft were warned. After the eruption, Anchorage airport cancelled hundreds of flights.

The ash particles that endanger aircraft are typically only a few micrometres in size — smaller than water droplets in clouds — so they are often invisible to weather monitoring systems. A worldwide system of nine Volcano Ash Advisory Centers detects ash plumes and advises pilots, but USGS scientists say more research is needed to refine particle-modelling capabilities to better detect plume presence and movement. Some of them are currently analysing ash found in their car park in Denver, Colorado, to see if it came from Mount Redoubt, 4,000 kilometres away.