Scientists are on high alert after spotting a key sign that a US volcano is about to erupt.
Huge plumes of steam have been seen rising from Mount Spurr, one of Alaska‘s largest active volcanoes.
Mount Spurr last erupted in 1992 but has been showing escalating activity for months, and the Alaska Volcano Observatory (AVO) now thinks a new eruption is likely.
The scientists monitoring the volcano believe an explosive eruption in as little as three weeks is the ‘most likely scenario’.
Mount Spurr, which is about 80 miles (128km) from Anchorage, stands at 3,374 metres (11,070ft) tall and is the highest volcano in the Aleutian mountain range.
In an update on March 26, scientists observed a ‘robust plume’ of steam rising from the summit.
Although the plume’s sudden formation is likely due to favourable weather conditions, the researchers say other signs point to an imminent eruption.
In an update, the AVO writes: ‘The increase in gas emissions confirms that new magma has intruded into the Earth’s crust beneath the volcano and indicates that an eruption is likely, but not certain, to occur within the next few weeks or months.’
Scientists are on high alert after observing a huge plume of steam rising from the summit of Mount Spurr (pictured), the highest volcano in Alaska’s Aleutian mountain range
The Alaska Volcano Observatory (AVO) says that the steam alone is not a sign of an impending eruption. However, combined with the emergence of new gas vents, or fumaroles, and increasing activity, scientists now consider an eruption likely
Mount Spurr consists of a large central summit and a major side vent about two miles (3.5km) to the south called Crater Peak, which has been the site of all major historical eruptions.
Over the past weeks, scientists and civilian observers have noticed a large ‘volcanic plume’ rising from the summit.
While this shows that the volcano is active, scientists maintain that this alone is not a sign of increasing risk.
According to the AVO, the visible appearance of the plume is most likely due to low wind speeds and cool, wet conditions which allow more steam to form.
On March 26, when the plume appeared largest, weather conditions were perfect for a steam plume to form.
The scientists write: ‘AVO’s analysis of satellite remote sensing and geophysical data from March 26 showed no notable changes.
‘These observations, in tandem with the favorable atmospheric conditions, suggest the robust plume from Mount Spurr in recent days was not a result of increased volcanic activity.’
However, although the visible plume was not a sign of impending danger, other key signals show the volcano could soon erupt.
Mount Spurr (pictured) is about 80 miles (128km) from Anchorage and stands at 3,374 metres tall (11,070ft)
Mount Spurr last erupted in 1992, producing a cloud of ash that stretched 12 miles (20 km) above sea level, closing airports, offices, and schools and costing nearly $2 million (£1.54 million) to clean up. Pictured: Mount Spurr erupting in 1992
Currently, the amount of gas being produced by Mount Spurr (pictured) means that an explosive eruption in the next few weeks is the most likely scenario
On March 7 and 11, the AVO flew aircraft over the summit and over Crater Peak to gather samples of gas rising from the volcano.
These flights showed that the Mount Spurr summit is now producing about 450 tonnes of sulphur dioxide every day.
That is nine times higher than measurements taken in December 2024 when the summit produced less than 50 tonnes per day.
The AVO also observed that the CO2 concentrations above the Crater Peak were especially high.
The scientists write: ‘In the past, such values have been observed prior to eruptions.’
Additionally, there are now over 100 earthquakes per week originating from beneath the mountain.
Since April 2024, there have been 3,400 earthquakes underneath Mount Spurr, indicating that magma is building up within a buried magma chamber.
Likewise, the AVO has observed that steam is now rising from places around the summit and Crater Peak, many of which have not steamed since 2008.
During a flight over Mount Spurr on March 7, the AVO recorded levels of sulphur dioxide over nine times higher than in December 2024, as shown in the red region on this graphic. The last time gas output was this high was shortly before a major eruption
The AVO has also observed steam emerging from areas around the site of previous explosions which (pictured) have not been active since 2008
The researchers monitoring the volcano now consider an explosive eruption the most likely outcome of this increasing unrest.
In 1992, an eruption followed just three weeks after these signs were first detected but the AVO also cautions that ‘an eruption could occur with little or no additional warning’.
Mount Spurr has been placed on a yellow/advisory warning since October 2024 but the AVO says it could issue an orange/watch or even a red/warning if further warning signs appear.
If an eruption were to occur, scientists predict it would be similar to the previous explosions which took place in 1992 and 1953.
In this scenario the most significant risk would be created by airborne ash clouds blasted into the atmosphere by the force of the blast.
The most recent eruption shot a pillar of ash rising 12 miles (20 km) above sea level, closing airports, offices, and schools and costing nearly $2 million (£1.54 million) to clean up.
Breathing in falling ash can also harm the airways and Alaskan residents are advised to wear a mask or remain inside in the event of an eruption.
Other hazards such as pyroclastic flows or mudflows known as lahars would be localised to the immediate area around Mount Spurr and generally pose little threat to local communities.
In recent months, there have been around 100 earthquakes per week beneath Mount Spurr (illustrated in blue). This prompted the AVO to issue a yellow warning (top) in November but this could rise to orange or red in the future
If Mount Spurr (pictured) were to erupt, the biggest risk would be posed by floating ash clouds which cause widespread disruption and are dangerous to human health. More lethal risks such as pyroclastic flows will be limited to the area immediately around the volcano
In a post on Facebook written on March 19, the AVO advised Alaskan residents on the risks of volcanic activity and how to stay safe in the event of an eruption.
The AVO wrote: ‘The major hazards to Alaska residents from Spurr would be from ash risk to aviation and possible ashfall.
‘The other hazards from a Mount Spurr eruption would only affect the areas immediately surrounding the volcano.
‘While there are no residents in the identified hazard areas for pyroclastic flows and lahars, people do visit the area for recreational or subsistence purposes.’