According to NASA researchers, the earthquake caused a tectonic shift that resulted in the downward movement of the island’s surface. This phenomenon, combined with a modest rise in sea levels, amplified the threat faced by small islands in general and particularly impacting approximately the 45,000 inhabitants of American Samoa.
Tutuila Island is Sinking Faster Than Before
Tutuila Island is the largest and most populous island of American Samoa. It is also the most affected by the earthquake-induced subsidence. A new study published in AGU’s Journal of Geophysical Research: Solid Earth shows that Tutuila Island experienced an annual average subsidence of 6 mm to 9 mm between 2015 and 2022, compared to a pre-2009 earthquake subsidence of 1 mm to 2 mm per year.
The researchers used satellite and terrestrial observations to measure the relative height and changes in the land. They used InSAR technology, which can penetrate clouds and dense vegetation, allowing them to accurately measure the land movement. They also incorporated satellite altimetry data to estimate ocean levels, connecting them with measurements from the tide gauge station in Pago Pago, the capital of American Samoa.
The Implications of Subsidence and Sea Level Rise for American Samoa
The study highlights the pressing need for immediate actions aimed at aiding small islands, which face the risk of disappearing due to the rising ocean surface. The researchers warn that the subsidence is likely to continue for decades, as the island adjusts to the post-earthquake tectonic changes.
The sinking of Tutuila Island has intensified its already rising sea levels, which are projected to increase by 0.5 m to 1 m by 2100. This poses serious challenges for the island’s infrastructure, coastal ecosystems, freshwater resources, and human settlements. The researchers suggest that adaptation strategies such as coastal protection, relocation, and elevation should be considered to mitigate the impacts of subsidence and sea level rise.
