Volcanic ash, aircraft don't mix

Do Hawaiian eruptions pose a threat to aircraft? The threat posed by ash injected into the atmosphere by explosive eruptions is so well known that seven centers have been established to monitor it worldwide. While jet engines run hot enough to melt any volcanic ash they ingest, engine parts can get coated and openings can get clogged, resulting in the complete shutdown of the affected engine. This is of enough concern to commercial airlines that the ash-threat centers maintain vigil, detecting and tracking volcanic ash clouds in order to redirect air traffic.

It remains one of the goals of the USGS to improve aircraft safety from the threat of volcanic ash.

Hawaiian eruptions are most often effusive and erupt lava, but they can also be explosive. Kīlauea had a series of ash-producing eruptions between 500 and 200 years ago and, most recently, in 1924. Anecdotal evidence suggests that Mauna Loa erupted ash in 1868. Obviously, explosive eruptions of Hawaiian volcanoes are much less frequent than lava-producing eruptions, but they do happen. Over the last several thousand years, Kīlauea has erupted explosively about as often as has Mount St. Helens. Therefore the probability of an ash-producing eruption in the Hawaiian Islands is low–about the same as it is for Mount St. Helens.

Explosive Hawaiian eruptions are easily capable of putting ash into the atmosphere at all elevations at which commercial aircraft fly. The ash produced by at least one of the Kīlauea events 200-500 years ago is believed to have reached altitudes of 9 km (30,000 feet) or more. One of the last eruptions in this series in 1790 produced an ash column that probably topped 5 km (16,000 feet). Of course, these events were slightly before aircraft were perfected, so those eruptions posed no threat. The most recent ash-producing eruption of Kīlauea in 1924 deposited significant amounts of ash 40 km (25 miles) away.

In the unlikely event that we do experience an explosive eruption, the threat to aircraft will be defined by how wind carries the ash and gas. Normal trade winds would carry most of this ash west of the Big Island, possibly affecting air traffic to the South Pacific and South America. If the ash column rises above about 6 km (20,000 feet), ash would get into the upper wind pattern and be carried to the northeast. Kona winds would also carry ash clouds to the north. Ash dispersal to the north could disrupt normal inter-island and mainland air traffic lanes.

In terms of everyday operations, explosive Hawaiian eruptions pose infrequent but significant threats to aircraft. Effusive eruptions, which are much more frequent in Hawai‘i, also produce airborne particles, but to much lower densities than explosive eruptions. The only incident of aircraft problems due to Hawaiian eruptions was the crash of a Bell 206 helicopter in November 1992 in the crater of Pu‘u ‘O‘o. The helicopter, which was carrying a film crew from Paramount Pictures, flew through the volcanic gas plume. The plume is known to be highly corrosive and low in oxygen, and the helicopter’s engine failed as a result of ingesting volcanic gas.

The threats posed to aircraft by effusive eruptions are just a severe as those posed by explosive eruptions, but only for the area immediately around the vent or vents. If you were wondering who would pilot a helicopter through the plume, rest assured that no local pilot would agree to do it. The film company brought in a pilot from the mainland to get what they needed. The helicopter made a hard landing inside the crater in Pu‘u ‘O‘o, and all inside were eventually rescued. And–you guessed it–this event was made into a TV movie.

Activity Update

Eruptive activity at Pu`u `O`o continues. Lava in the Banana flow, which breaks out of the Mother’s Day lava tube a short distance above Pulama pali, has been visible between the pali and Paliuli for the past several weeks. The viewing during darkness has been good but distant. Eruptive activity in Pu`u `O`o’s crater is weak, with sporadic minor spattering.

No earthquakes were reported felt on the island during the week ending August 25.

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity was notably high for the fifth week in a row, with 31 small earthquakes recorded in the summit area. The activity was lower than during the previous week, however, when 80 earthquakes were recorded. Most of the earthquakes are of long-period type and deep, 40 km (23 miles) or more.

This article was written by scientists at the U.S. Geological Survey’s Hawaii Volcano Observatory and is republished by HawaiiNews.com with permission.

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