AVO maintains networks of seismometers on a subset of Alaskan volcanoes. The networks consist of a few to several short-period vertical and three-component instruments. Data is
passed in near-real time through radio telemetry and telephone lines to recording and analysis laboratories at UAFGI and USGS-Anchorage.
Seismology lab, University of Alaska Fairbanks, Geophysical Institute.
Typically, the reawakening of a volcano can be seen by the increased rate of background seismicity over a period of months or weeks as new magma works its way upward beneath the
volcano, displacing and breaking the countryrock. (Volcanic earthquakes are typically quite small - with maximum magnitudes of 2 or 3). As the eruption nears, seismologists may see a unique type of volcano
seismic activity (called long-period events) associated with degassing of the rising magma. Finally, as an eruption begins, the strong seismic signals generated by the explosive eruption itself can bee seen.
This permits accurate determination of the time of onset of an eruption, even in the dark or during poor weather, which is critical information for agencies concerned with the safe operation of aircraft above and
many hundreds of kilometers downwind from the volcanoes.
Seismic activity is monitored in real time at 30 volcanoes in Alaska: Wrangell, Spurr, Redoubt, Iliamna, Snowy, Griggs, Katmai, Novarupta, Trident, Mageik, Martin,
Peulik, Ukinrek Maars, Aniakchak, Veniaminof, Pavlof, Dutton, Isanotski, Shishaldin, Fisher, Westdahl, Akutan, Makushin, Okmok, Korovin, Great Sitkin, Kanaga, Tanaga, and
Gareloi volcanoes. Many seismometers are located on each of these volcanoes and the data is telemetered to Anchorage and Fairbanks in real time
for processing and analysis.
AVO SEISMOLOGY IN THE FIELD
The following is a daily project log from the 1996 summer expansion of the Pavlof - Dutton seismic network, Unalaska Island, Alaska.
Monday June 17 - Seismology crew - Steve McNutt (chief), Guy Tytgat, and John Benoit - arrive in King Cove. Helicopter and pilot arrive about 5pm.
Tuesday June 18 - Dutton station DT2 disassembled but not removed because weather forced helicopter away from site. Site prep. at one of the Pavlof station
Wednesday June 19 - Barge with seismic station enclosures and other gear arrived about 1:30 pm (a few days late). Air freight, including electronic test equipment and
tools, still has not arrived. Weather begins to deteriorate.
Thursday June 20 - Air freight is all in at Cold Bay, and a substantial portion has been transferred to King Cove. The transfer process is in our hands. 500' ceiling and
continued marginal weather expected.
Friday June 21 - Weather was clear enough on the north side of the Alaska Peninsula to fly in some gear and begin site preparation on the north side of Pavlof. Low ceiling
and drizzle persisted in King Cove.
Site preparation at PN6.
Barge with station enclosures and other gear arrives in King Cove.
Guy and Steve watch Lloyd Schumacher unload the barge.
Monday June 24 - All equipment has been moved to King Cove. Batteries have been put at northern sites. Equipment huts mostly completed
antennas and solar panels mounted. Electronics assembly well advanced. Weather continues to be marginal.
Steve McNutt and Guy Tygat prepare one of the seismic station huts.
Tuesday June 25 - Rain expected to continue for the next several days. Almost all of the work that can be completed in town is done. Local residents say this June
has had unusually poor weather.
Wednesday June 26 - Run-of-the-mill Aleutian weather is wet, windy, and cool, as this view of Lenard harbor (between Cold Bay and King Cove) suggests. The
Aleutian Islands and Alaska Peninsula form a mountainous fence between the Pacific Ocean and Bering Sea. Moist air moving from either water body
rises and condenses when it encounters the mountains, forming clouds which hang on the mountain tops during most of the year. The parade of low pressure systems which form in the western Bering
Sea and march relentlessly into the Gulf of Alaska assure that there is a nearly continuous supply of moist air moving towards land from one direction or another.
Low pressure across the entire state.
Where does the parade of lows come from? Ocean currents in the North Pacific move clockwise, bringing warm water up past Japan towards the western Bering Sea. A
boundary layer of warm, moist air travels with the ocean currents. In the western Bering Sea the warm water and air meets cold air and water from the northern Bering Sea.
The warm wet air rises upward over the cold air, spinning counterclockwise because of Coriolis forces. This is the birth of the cyclonic low-pressure system. As the warm air
rises it condenses, and that condensation releases latent heat which increases the buoyancy of the air mass which intensifies the cyclonic circulation. The cyclone then
drifts off to the east (across the Aleutians and into the Gulf of Alaska) in response to global circulation patterns. My thanks to Jeff Tilley of the UAF/GI for explaining this to
Guy Tygat prepares repeater electronics for installation on Douglas Island. (6/27/96)
Thursday June 27 - The weather is still not great, and the crew spent some constructive time assembling electronics. The pilot, Glen Gulick, had the day off. In
Alaska we feel we have to apologize for taking any time at all off during the summer. Field seasons are so short that we tend to work 'til we drop when we can, and rest up on weather days or in the fall (or - more and more -
when the helicopter money is used up). The FAA, however, insists that pilots take some scheduled time off once in a while. We agree that's a good idea in light of the seriousness of the
mistakes that might be made by a tired pilot.
Guy and John bolt solar panels to PVV. PVV, the first station to go on the air, began sending data at 17:30 on June 29th, 1996.
Friday June 28 through Monday July 1 - The weather improved dramatically and the seismic field crew swung into high gear.
They flew 7.4 hours on Saturday, and that is a whole lot for helicopter work. The crew barely slowed down enough to let us know how they were doing or to take the time to
FTP more photographs. Three stations on the south flanks of Pavlof and a repeater station on Dolgoi Island are now working.
With the installation of the repeater on Deer Island (the next task) data could begin flowing to AVO seismic laboratories in Fairbanks and Anchorage.
PS1 seismometer in the hole. This is the instrument that measures the ground shaking which we use to monitor active volcanoes.
Wednesday July 3 - Workable weather continues. Seismology crew now has 3 stations out on the S flank of Pavlof Volcano, one station on Dolgoi Island which
repeats the Pavlof signals to Deer Island, where another seismometer is installed and where the southern half of the net is repeated into King Cove. As I type they are trying
to install a couple of the stations on the northern side of Pavlof, which will nearly complete their job. We can't show you any photos quite yet, since the crew is moving
too fast to ftp the photos. They assure me they have some good ones to post in a few days.
Batteries, electronic components, and antenna inside the PS4 enclosures.
Aside - In times of hectic activity, be it from an eruption or seismic crisis or a spate of good weather in the field, there is little time for activities such as this web page. When we have the most to report we
have the least time to report it. We have the added factor of lots of daylight here. Except for the limits on consecutive pilot flight hours, there is little to keep us from putting in very long days. One of the real
luxuries of field work in lower latitudes is that you HAVE to stop when the sun goes down, which provides time to stop and think and recharge every day. But then we have all winter to recharge.
Tom Miller is in the field working on the geology of Dutton Volcano. Dutton is not well a known volcano, but consists of a central dome complex which has, in Holocene time,
shed large debris avalanches, especially to the south. A seismic swarm similar to the March, 1996 swarm at Akutan, resulted from the emplacement of a dike of new
magma beneath Dutton.
Friday July 5 - Rain and low clouds returned, leaving the field crew with time to send in many images.
July 12. This portion of the project is finished. Seismic station installation is complete. During the final part of this portion of the project Tom Miller, Darren Chertkoff, and John
Eichelberger worked on the geology and petrology of Dutton Volcano and Emmons Caldera. Tom completed his mapping of the area and introduced Darren and John to
fabulous Lassen-like magma mixing at Dutton and Yellowstone-like tuffs at Emmons.
Dolgoi Island seismic station with Pavlof Volcano in the background.
July 13-14. Tina Neal and Guy Tytgat intercepted the helicopter in Port Heiden as it moved from King Cove to King Salmon. They checked on the single Aniakchak
seismic station, which had stopped working during the winter. It was severely abraded by wind-borne debris. Tina was also able to do some final field checking of her
geologic map of the caldera.