Scientists closely monitor earthquakes in American Samoa

American Samoa has flown in experts to monitor seismic activities in the territory, after ongoing earthquake swarms prompted alarm over a possible volcanic eruption. 

For weeks, earthquakes have rattled the Manu’a Islands, with residents reporting shaking and jolts of varying intensity since 26 July.  

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.

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”.

It described Vailulu’u as “an unpredictable and very active underwater volcano, presenting a potential long-term volcanic hazard”.

Vailulu’u — 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)

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.