A European earth observation satellite captured imagery of what appears to be waves spreading after an underwater volcano erupted off the island nation of Tonga on January 15.

The satellite passed near Tonga and collected data about 13 hours after the eruption. The satellite's radar allows detailed observation of Earth's surface and changes in sea surface.

Tofua Island, which is about 100 kilometers north of the volcano, is near the center of the imagery taken from the satellite. Semicircular waves can be seen spreading over dozens of kilometers around the island.

Professor Mori Nobuhito at the Disaster Prevention Research Institute of Kyoto University is an expert on tsunamis and high waves. He said the imagery captured the sea-surface change after the eruption.

Mori pointed out that each wave was up to five kilometers apart from the next one, which is a much narrower interval compared with tsunamis generated by earthquakes.

He said this led to a shorter period between each wave, which corresponds with what was indicated by the data collected by tide gauges at various locations after the eruption.

Mori said this observation is very rare, and the data is important to help understand how the sea surface changed after the eruption.

He added that if the intervals are shorter, waves tend to move in a complicated way, as they are reflected over terrain.

Mori said waves with shorter intervals were apparently traveling back and forth in the Pacific even half a day after the eruption, which possibly led to the waves of various heights that were observed around Japan.

He also said the sea-surface change was a very rare and complicated phenomenon caused by multiple factors, including a change in atmospheric pressure after the eruption.

He said that he believes the spatial data will lead to a deeper understanding of the entire phenomenon.