Below the green discoloration lies Kaitoku Volcano
Photo: NASA Earth Observatory
When Kaitoku wakes up, the water changes color.
The volcano is located north of the Japanese island of Iwo Jima, hidden in the Pacific.
There are a good hundred meters between its three peaks and the water surface.
When the volcano is active, it leaves telltale traces.
Clearly visible in the deep blue of the ocean, greenish discolorations suddenly appear.
They are probably formed by rising, superheated, acidic seawater containing volcanic rock debris and sulphur.
Around the world in 99 minutes
The easternmost of the three craters has been active since the summer, the other two have long been extinct.
The photo is from early January.
It comes from the "Landsat 8" earth observation satellite, which orbits the earth once in 99 minutes and flies at an altitude of 700 kilometers.
It takes 16 days to scan the entire surface of the earth.
Kaitoku is just one of many active underwater volcanoes on Earth.
It is estimated that there are 25 million seamounts formed by volcanic activity, most of which are extinct.
However, those that are still active account for much of the world's volcanic activity.
Geologists estimate that around 80 percent of all volcanic eruptions take place under water.
The last significant eruption of Kaitoku was almost 40 years ago.
Historical records indicate that the volcano also erupted in 1543.
Compared to other underwater volcanoes, however, it is considered less dangerous.
58 km high column of ash and gas
One of the most spectacular eruptions of an underwater volcano happened a good year ago.
On January 15, 2022, the Hunga Tonga-Hunga Ha'apai volcano ejected hot gases and clouds of ash that stretched miles into the sky.
An explosion followed the next day, which was more violent than the most powerful atomic bomb, never before has a more violent one been measured.
The column of ash and gas rose 58 kilometers into the stratosphere.
The blast wave moved around the world multiple times.
The Tonga volcano's eruption was so massive that it obliterated parts of nearby islands.
According to data from satellites, material from the eruption cloud was still circulating in the stratosphere a year later.