New islands appear after Indonesia's Anak Krakatau volcano erupts

Two new islands have emerged in waters surrounding Mount Anak Krakatau following a major eruption last month that grounded flights for days, the head of Indonesia's volcano monitoring agency said Friday.

The islands were spotted in satellite images of the water-filled caldera in which Anak Krakatau stands, Rita Susilawati of the PVMBG Centre for Volcanology and Geological Hazard Mitigation told AFP.

"Based on an evaluation of Sentinel satellite imagery, two formations resembling small islands can be seen around Mount Anak Krakatau" in the Sunda Strait between Java and Sumatra islands, she added.

Sentinel is a fleet of Earth observation spacecraft developed by the European Space Agency.

One of the islands was located about 760 metres northwest of Mount Anak Krakatau, the other about 495 metres southwest.

Rita said it was too early to refer to the islands as "children" of Mount Anak Krakatau -- which itself was formed by an underwater eruption in the caldera or depression left behind after the massive 1883 blowout of the original Krakatau volcano.

"Anak" means child in Bahasa Indonesia.

Rita said further research was needed to determine if the new islands were emerging from the base of the caldera in a similar way than Anak Krakatau did, or whether they were formed by deposits of volcanic material.

In the case of Anak Krakatau, several landmasses briefly emerged starting in 1927 and then disappeared due to erosion before an enduring island formed in 1930, she added.

The two new islands may similarly be eroded away over time.

Mount Anak Krakatau erupted for 25 hours non-stop in September, blanketing cities in volcanic ash and prompting multiple airports to close.

More than 300,000 passengers were left stranded.

Rita said Anak Krakatau was at alert Level 2, the second lowest out of four danger categories.

People are advised not to approach within three kilometres (1.86 miles) of the eruption centre.

Five journalists on a mission to cover the September eruption were declared presumed dead with three boat crew nearly two weeks after the vessel they were travelling in disappeared without trace.

Indonesia sits on the Pacific Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity.