Following an increase in small earthquakes under Augustine Volcano last week, the Alaska Volcano Observatory in Anchorage raised the level of concern for Augustine Volcano from code green to code yellow. Scientists also have measured a 1-inch bulge in the volcano's dome.

In its four-level system, code yellow means the volcano is restless and the potential for an eruption has increased. Gas and steam plumes with minor amounts of ash also are possible.

Augustine last erupted with a series of explosions that started March 27, 1986. Historically, Augustine is more active than the other Cook Inlet volcanoes — Iliamna, Redoubt and Spurr — said Chris Waythomas, a geologist at the observatory. Augustine is also known to have erupted in 1812, 1883, 1908, 1935, 1963-64 and 1976.

“"It wouldn't be a big surprise if it should erupt again,"” he said. "“The one nice thing is almost always it has some precursor of seismic activity.”"

The biggest danger to Homer and the lower Kenai Peninsula is from ash fall — the worst and most irritating effect from the 1986 eruption. Drifting ash clouds can be dangerous to aircraft, particularly jets. Hot clouds of gas and ash that roar down a volcano's slope can be extremely dangerous to nearby boats and low-flying aircraft, or anyone on the island.

A tsunami generated by a landslide or eruption from Augustine is not as high a concern, Waythomas said. For a tsunami to happen, part of the mountain would have to collapse and fall into the sea. The effect of a tsunami would also depend on the tide. If Augustine did collapse, the amount of debris wouldn't likely cause a large tsunami. It also would go to the north-northwest and affect mostly the opposite side of the inlet, Waythomas said.

“"I'm not saying it's impossible, but the things that have to occur for it to produce a large, damaging wave — they just don't happen very often,"” he said.

An avalanche from the 1883 eruption of Augustine did flow into Cook Inlet and might have caused a tsunami seen at Nanwalek.

The Alaska Volcano Observatory is coordinating with the Alaska Tsunami Warning Center in Palmer to advise the public in the event of a tsunami, Waythomas said.

Since last May, the number of magnitude 1 or less earthquakes from about a mile under Augustine has increased from four to eight a day to 20 to 35 a day. The 1-inch bulge measured on the volcano is the first since instruments were put on the volcano before the last eruption in March 1986.

“"It's a small amount, but it looks to be real,"” Waythomas said.

Augustine is one of the most widely measured volcanoes monitored by the observatory. Geodetic, or ground movement measuring, instruments are all around the island, as well as numerous seismometers to measure earthquakes.

“"We've got this volcano wired,"” Waythomas said. "“If it wiggles, we know... We're taking its heartbeat.”"

A Web camera also has been set up near Bluff Point at the top of Baycrest Hill. Scientists plan to take a flight to the volcano this week to check for temperature changes on the mountain using a FLIR, or forward looking infrared, detection system, the same device Alaska State Troopers use to look for heat signatures of missing people.

To view the Webcam or check for further updates, go www.avo.alaska.edu. Scientists have not seen recent ash or steam from Augustine. Reports of ash or steam can be called in at (907) 786-7497.

Michael Armstrong can be reached at michael.armstrong@homernews.com.