(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

How do you know when a volcano is exploding? “Just look at it” seems like the obvious answer. 

This works if there are some eyes aimed at the volcano in question, and if those eyes can see the volcano. But many volcanoes are located in remote areas, where eyes are in short supply. 

Whether they are remote or not, some volcanoes are chronically obscured by inclement weather or persistent clouds. And all volcanoes are obscured when the sun goes down. These factors combine in some parts of the world. 

One such place is Alaska, which has more than its share of remote volcanoes, some of the worst weather on the planet, and — in winter — extended periods of darkness. The combination often makes eruption detection a challenge. 

Why should we care whether or not a remote volcano in Alaska is exploding? There was indeed a time when it would have been of little consequence. 

But today, airliners carry a daily total of about 15,000 passengers across the north Pacific, and Anchorage, Alaska, is one of the busiest air cargo hubs on earth. Most of these passenger and cargo planes pass near some of Alaska’s 50 historically active volcanoes, many of which are capable of projecting volcanic ash to heights well above airline cruising altitudes. 

Furthermore, Anchorage — Alaska’s largest city — is subject to ash fall from a number of volcanoes west of Cook Inlet. 

Ash-producing eruptions — or even the threat of ash-producing eruptions — can cause serious social and economic disruptions. In Alaska, it is the responsibility of the Alaska Volcano Observatory (AVO) to minimize these disruptions by forecasting eruptions and providing warnings when eruptions do occur. 

Like HVO, AVO routinely employs a combination of seismometers, GPS instruments, Web cameras, satellite imagery, and other instruments to provide forecasts and warnings.   

The awakening of Redoubt Volcano in late January of this year provided a nearly ideal opportunity to test the USGS Volcano Hazard Program’s new transportable Doppler radar system and to extend AVO’s monitoring toolkit. The radar was installed at the Kenai Municipal Airport, about 50 miles east of Redoubt — about 62 miles southwest of Anchorage. This site offered an unobstructed view of Redoubt, as well as the support of the airport staff and the City of Kenai. 

An additional important advantage of the airport is its proximity to an FAA (Federal Aviation Administration) NEXRAD Doppler radar. NEXRAD radars — some operated by the FAA and others operated by the National Weather Service — produce most of the weather radar images you see on television and on the Internet. So data from the USGS radar could be compared to data from NEXRAD.   

The USGS system first became functional March 20, roughly a day before the first of a series of explosive ash-producing eruptions of Redoubt. 

Despite the inevitable start-up problems, nearly all of the eruptions were monitored by the radar remotely operated from AVO offices in Anchorage. Eruption plumes were detected within less than a minute, and plume heights and the direction of falling ash were monitored. The data compare favorably to data from NEXRAD. 

Some of the eruptions shot ash to altitudes greater than 60,000 feet — more than four times the elevation of Mauna Kea — and deposited ash on Alaskan communities. Air traffic and community life were disrupted, but timely warnings minimized the impact. 

The USGS radar will remain in Kenai until Redoubt lapses into repose. Past behavior suggests that this could take months. Subsequently, the system will be available wherever it’s needed within areas of USGS responsibility. The next deployment is apt to be in the lower 48, in the Northern Marianas, or even in Hawaii.