American Samoa has flown in experts to monitor seismic activities in the territory, after ongoing earthquake swarms prompted alarm over a possible volcanic eruption.
Key points:
- Residents from the Manu’a Islands have been feeling earthquakes since July 26
- Small earthquakes can be an indication of the beginning of a new volcanic eruption
- Experts say the nearby volcanoes are very different to those in Tonga and tend to have smaller-scale eruptions
For weeks, earthquakes have rattled the Manu’a Islands, with residents reporting shaking and jolts of varying intensity since July 26.
According to the US Geological Survey (USGS), the earthquakes are most likely related to the Ta’u volcano or the nearby underwater Vailulu’u volcano.
“It is also possible that the swarm is an early precursor to an eventual eruption,” analysis from USGS says.
Similar activity was reported in the lead-up to Tonga’s devastating volcanic eruption in January, but experts say a large volcanic explosion of that kind is unlikely.
The USGS says more investigation is needed and teams of scientists are currently on the ground closely monitoring the activity.
Should American Samoa and its Pacific neighbours be worried? This is what we know so far.
Large eruption unlikely
The American Samoa government has activated the National Emergency Operation Centre (NEOC), telling local officials in the Ta’u and Ofu islands to prepare assistance “in case something happens”.
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It described Vailulu’u as “an unpredictable and very active underwater volcano, presenting a potential long-term volcanic hazard”.
When Tonga’s underwater Hunga Tonga-Hunga Ha’apai volcano erupted on January 15, it caused the largest explosion documented by researchers since 1883.
It sent more than 58,000 Olympic-size swimming pools’ worth of water vapour into the stratosphere, and triggered a devastating tsunami which wiped out entire islands.
Professor Shane Cronin from Auckland University said it was understandable that people would be concerned about submarine eruptions after Tonga.
However, he assured that the chain of volcanoes in the American Samoan islands are very different to those in Tonga.
In Samoa, the volcanoes usually produce a gentle eruption, similar to what is seen in Hawaii, with small lava flows or mild explosions.
“The Tonga volcano was a very, very major event that doesn’t happen very often,” Professor Cronin told the ABC’s Pacific Beat program.
“Most volcanic eruptions are much smaller and much more manageable.”
Although small earthquakes can be an indication of the beginning of a new eruption, they could also just be related to adjustments of tectonic plates in the area, Professor Cronin said.
He predicts that the earthquakes could continue for quite some time.
Professor Cronin’s comments mirror initial analysis from the USGS, which said an eruption would most likely include slow-moving lava flows or low-level explosions of lava that are localised to a small area.
“I would be surprised if it would affect many areas with volcanic ash or other other types of deposits,” Professor Cronin said.
Vailuluʻu — which is located 40 kilometres east of Ta’u — last erupted in 2003, during which a cone formed within the summit caldera, according to the USGS Hawaiian Volcano Observatory (HVO)
How should locals prepare?
American Samoa’s volcanoes are monitored remotely by satellites and an earthquake detection station in Apia, in neighbouring Samoa.
According to the USGS, these instruments might detect significant explosive activity in American Samoa, but the lack of ground-based monitoring stations at the volcanoes does not allow for advanced warning of new activity.
Over the weekend, the USGS joined a team of experts from the National Oceanic and Atmospheric Administration (NOAA), the Pacific Tsunami Warning Centre and NOAA-IOC International Tsunami Information Center, on the ground, to better understand the series of earthquakes.
Additional teams from the HVO are also consulting with local authorities on the situation.
Professor Cronin said that, right now, the best way to prepare for a possible eruption is the same as in any other natural disaster.
“It’s about just being ready, being aware, having all your valuables ready, and so on, if there is need for evacuation,” he said.
“And just keeping an eye out on the signs and signals of what’s going on and listen to what authorities are saying.”
In September 2009, two large earthquakes between Samoa and American Samoa triggered a tsunami that generated waves of up to 22 metres.
At least 192 people were killed, including 149 in Samoa, 34 in American Samoa, and nine in Tonga’s Niuatoputapu.