This week in the south-west Pacific, an ash cloud rising from Indonesia’s erupting Sangeang Api volcano has resulted in the cancellation of flights over northern Australia, and in the north-east of the same ocean, the threat of a major eruption hangs over Alaska’s Pavlof volcano.
Pavlof Alert in Alaska
On June 2, the United States Geological Survey raised the alert for Pavlof to the highest level.
The alert, which is in two parts, consists of a volcano alert level, currently set at ‘warning’ – indicating that “hazardous eruption is imminent, underway, or suspected” – and an aviation colour code, currently set at red – which means that “Eruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere .”
Although Pavlof last erupted as recently as June 2013, the alert level was reduced to green in August of that year and remained at that level until 31 May 2014, when it was raised to amber (the second highest) following a low-level eruption. The escalation of this eruption led to the increased alert and concerns about possible hazards to aviation.
Pavlof and the Aleutian Chain
Pavlof is just one of almost 100 active or recently-active volcanoes in Alaska, most of them forming the Aleutian island chain which runs in an arc along the Alaskan subduction zone.
Part of the so-called Pacific Ring of Fire, this line of volcanoes results from the downwards movement of the dense Pacific plate as it meets the North American plate.
The ocean crust melts as it descends to great depths in the mantle. The molten rock, more buoyant than the overlying rock, rises and reaches the surface as lava – and creates a chain of volcanoes behind the actual plate margin. The Aleutian islands are a classic example of such a a volcanic arc.
Eruptions are by no means uncommon and at the time of writing three other Alaskan volcanoes are under either amber or yellow watch. Pavlof itself has been regularly active; the GVP database includes 21 confirmed eruptions since 1950, several of them erupting large volumes of lava and lasting for anything from one day to several months.
Ash Clouds and Aviation Hazard
Despite the levels of volcanic activity (according to the Smithsonian Institution’s Global Volcanism Program “only Indonesia, Japan, and South America have had more volcanoes erupt during the past 100 years”) past eruptions have had limited impact on humans.
Most of the islands are uninhabited and so the degree of hazard is very low. Indeed, again according to the GVP, fatalities have been recorded from only three Alaskan eruptions.
Times are changing – and an eruption in an uninhabited part of the north Pacific will no longer go unnoticed. In a modern, increasingly digital, age, even remote volcanoes have an increased level of hazard.
The 2010 eruption of Iceland’s Eyjafjallajokull, which closed large parts of European airspace for days with consequent travel disruption and economic losses, raised awareness of the vulnerability of air traffic to volcanic ash and extended the understanding of a volcanic hazard well beyond the immediate surroundings.
Ash is a problem for aviation not just because it can impair visibility, but because the fine, abrasive particles can be sucked into jet engines and, melting, cause them to become clogged and to stall. Although to date there are no known cases in which volcanic ash has brought an aircraft down, there are several documented incidents of engines stalling and disaster narrowly averted.
For this reason, aviation authorities sit up and take notice when a major eruption occurs – and Alaska is overflown by many commercial flights between the US and parts of Asia, meaning that these remote volcanoes are increasingly monitored.
Pavlof’s Aviation Hazard
At present there is no expected disruption associated with Pavlof, despite reports that its plume has reached heights of around 22,000 feet. The current aviation advisory indicates reduced visibility and light ash fall in the immediate vicinity of the volcano. But if the eruption continues or strengthens, and depending on atmospheric conditions, the situation may change – and a few more people may start to notice what’s happening way up north.
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