THEWEATHERMOGIL:: When geology and meteorology meet
Another, not-so-unusual, relationship involves geology and meteorology. At the Earth-atmosphere interface, mountains and coastlines affect wind flow; mountains can lead to rain-shadow effects (wet on one side of the mountain and dry on the other); changes in elevation and/or the mountains themselves can lead to intense thunderstorm rainfall and flash flooding; and terrain, even without a mountain presence, can help to channel precipitation runoff into narrow canyons or waterways and lead to significant localized and/or deadly flash flooding.
Add volcanoes to the mix and now the geologic events themselves can cause meteorological impacts. The recent eruption of the Pavlof volcano in the Aleutian Island chain is a prime example (Fig. 1).
First, any heating of the exterior or near exterior of a volcanic mountain (which in northern climes is often ice and/or snow covered), can lead to rapid snowmelt and cause avalanches, mudslides and/or flooding. It is easy to see the effect that melting has in this image of the Pavlof volcano (Fig. 2).
The main risk from volcanoes happens during and following an eruption. Based on the force of the ejected air and gas cloud, volcanic dust and particles can be lifted to altitudes high above the Earth’s surface. The Pavlof eruption of last weekend was relatively “tame,” sending ash only four to five miles aloft. The eruption of Mount Pinatubo (June 1991) sent ash so high that it reached well into the stratosphere, where ash was still detected years later.
The eruption process, once started, resembles the convective process of regular thunderstorm formation. In fact, volcanic clouds, as they grow from the eruption, often look like “dirty” thunderstorm clouds (towers, anvils, precipitation, virga and/or “fall” streaks, lightning and sometimes waterspouts). Fig. 1 and Fig. 3 typify what volcanic thunderstorms look like.
In the short-term, volcanic ash and dust can lead to significant aviation impacts. In 1982, British Airlines Flight 9, flying at 37,000 feet, entered an ash cloud near Jakarta, Indonesia. The flight crew was not aware that such an ash cloud was in their flight path. As a result, the plane’s four engines “flamed out” and the plane started a growingly steep descent. The pilot was able to restart the engines, but not until the plane had descended to 12,000 feet. Following another “flame out” of one engine, the pilot was able to safely land the plane. A review following the incident demonstrated that the ash cloud was associated with an eruption from Mount Galunggung, some 110 miles southeast of Jakarta.
A similar experience occurred in late 1989 following an eruption of Mount Redoubt, AK. Here, a KLM flight, carrying 231 passengers to Anchorage, suffered a drop of several thousand feet following a “flame out” of its engines.
Since the ash cloud plume from the recently-erupted Pavlof volcano extended several hundred miles into Alaska (Fig. 4), flight operations at Alaska Airlines were put on hold (41 cancellations) on Monday. With the volcano eruption lessening, and the threat level lowered accordingly, flight operations at Alaska Airlines are expected to resume yesterday.
As noted by Alaska Airlines spokeswoman Bobbie Egan, and most likely echoed by every airline executive worldwide, “We just simply will not fly when ash is present.”
Now, the United States Geologic Survey (USGS) routinely monitors volcanoes for all types of hazards and issues advisories or alerts for a wide range of target audiences. The USGS and other agencies use a sophisticated array of sensors to track earth movements, changes in lava distribution and aircraft to monitor actual or imminent eruptions. In the U.S., NOAA routinely provides satellite support, helping to track any ash clouds and monitor their density. Worldwide, a total of 9 Volcano Ash Advisory Centers (VAACs) provide such support for international aviation. The bottom line is that flight cancellations rather than emergency landings or actions are now the rule.
Although the Pavlof volcano has calmed down a bit and alert levels have been lowered, Pavlof and several other volcanoes worldwide remain on active USGS monitoring lists.
© 2016 H. Michael Mogil
Originally posted 3/30/16; updated 3/31/16