In late December 2014, a submarine volcano in the South Pacific Kingdom of Tonga erupted, sending a violent stream of steam, ash and rock into the air. The ash plumes rose as high as 30,000 feet (9 kilometers) into the sky, diverting flights. When the ash finally settled in January 2015, a newborn island with a 400-foot (120-meter) summit nestled between two older islands – visible to satellites in space.
The newly formed Tongan island, unofficially known as Hunga Tonga-Hunga Ha'apai after its neighbors, was initially projected to last a few months. Now it has a 6- to 30-year lease on life, according to a new NASA study.
Hunga Tonga-Hunga Ha'apai is the first island of this type to erupt and persist in the modern satellite era, it gives scientists an unprecedented view from space of its early life and evolution. The new study offers insight into its longevity and the erosion that shapes new islands. Understanding these processes could also provide insights into similar features in other parts of the solar system, including Mars.
"Volcanic islands are some of the simplest landforms to make," said first author Jim Garvin, chief scientist of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Our interest is to calculate how much the 3D landscape changes over time, particularly its volume, which has only been measured a few times at other such islands. It's the first step to understand erosion rates and processes and to decipher why it has persisted longer than most people expected."
The Tongan island is the third “surtseyan” volcanic island in the last 150 years to emerge and persist for more than a few months. Surtsey is an island that began forming during a similar kind of explosive, marine eruption off the coast of Iceland in 1963.
From the Tongan island’s beginning, it was tracked by monthly, high-resolution satellite observations, both with optical sensors and radar, which sees through clouds. Alerted to the volcanic eruption by NASA's Rapid Response program for the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, Garvin and his colleagues directed satellites to observe the island as soon as the eruption ended. Using this imagery, the research team made three-dimensional maps of the island’s topography and studied its changing coastlines and volume above sea level.
The team has calculated two potential scenarios affecting its lifetime. The first is a case of accelerated erosion by wave abrasion, which would destabilize the tuff cone in six to seven years, leaving only a land-bridge between the two adjacent older islands. The second scenario presumes a slower erosion rate, which leaves the tuff cone intact for about 25-30 years.
In April 2015, we watched an isthmus bridge begin forming from the new island to the older island neighboring it to the east. Soft volcanic material, especially on the island’s southern side, was eroded by the ocean and deposited on the tail end, which grew and grew till it reached the other island. It’s about 1600 feet (500 meters) across, or the length of 5 football fields.
The erosive forces of the ocean broke down the southern wall of the crater lake in May 2015. We thought this might mean that the island wouldn’t last much longer because the ocean could now attack the interior of the island’s tuff cone. But in June, a sandbar formed, closing off the lake again and protecting the interior. The sandbar has been in place ever since.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 220.127.116.11.0