JAKARTA • The volcano that triggered a deadly tsunami in Indonesia late on Saturday emerged from the sea around the legendary Krakatoa 90 years ago and has been on a high-level eruption watchlist for the past decade. The volcano is spelt as Krakatau in Indonesia.
Anak Krakatau, or Child of Krakatau, has been particularly active since June, occasionally sending massive plumes of ash high into the sky. In October, a tour boat was nearly hit by lava bombs from the erupting volcano.
Experts say Anak Krakatau emerged around 1928 from the caldera - a volcanic feature formed by the collapse of a volcano into itself - of Krakatau, a volcanic island that erupted violently in 1883. With subsequent lava flows, it grew from a submarine setting to become a small volcanic island, with the cone now standing at an altitude of around 300m above sea level.
Since its birth, Anak Krakatau has been in a "state of semi-continuous eruptive activity", growing bigger as it experiences eruptions every two to three years, volcanology professor Ray Cas of Monash University in Australia told AFP.
"Most of the eruptions are relatively small on the scale of explosive eruptions... and there are also eruptions that produce lava flows," he added.
Prof Cas said the latest event appeared to be "a relatively small explosive eruption" but could then have triggered or coincided with a submarine event like a landslide or earthquake, causing the deadly tsunami. No one lives on the island, but the peak is popular with tourists and is a major study area for volcanologists.
The island is part of the Ujung Kulon National Park, "demonstrating ongoing evolution of geological processes" since the Krakatau eruption, Unesco says on its World Heritage site listing for the area.
When Krakatau erupted on Aug 27, 1883, it shot a column of ash more than 20km into the air in a series of powerful explosions that were heard in Australia and up to 4,500km away near Mauritius.
The massive cloud of ash plunged the area into darkness for two days. The dust gave rise to spectacular sunsets and sunrises around the world the following year and disrupted weather patterns for years.
The tsunami triggered by the eruption killed more than 36,000 people in one of the world's worst natural disasters.
The archipelago nation has nearly 130 active volcanoes, forming part of the Pacific "Ring of Fire" - an arc of intense seismic activity.