"WASHED AWAY"

Television footage showed how the tsunami washed away an outdoor stage where Indonesian rock band Seventeen was performing for hundreds of guests at an end-of-year party for state utility company PLN.

At least four band members and support crew were killed, lead singer Riefian "Ifan" Fajarsyah told followers in a tearful Instagram account. The band's drummer was among the missing.

Another 29 PLN employees and relatives were also killed.

Anak Krakatau, roughly halfway between Java and Sumatra, has been spewing ash and lava for months. It erupted again just after 9 p.m. on Saturday and the tsunami struck about 30 minutes later, according to the Meteorology, Climatology and Geophysics Agency (BMKG).

The tsunami was caused by an undersea landslide resulting from volcanic activity on Anak Krakatau and was exacerbated by abnormally high tides because of the full moon, Nugroho said.

Ben van der Pluijm, an earthquake geologist and professor at the University of Michigan, said the tsunami may have been caused by a partial collapse of Anak Krakatau.

"Instability of the slope of an active volcano can create a rock slide that moves a large volume of water, creating local tsunami waves that can be very powerful. This is like suddenly dropping a bag of sand in a tub filled with water," he said.

The eruption of Krakatau, previously known as Krakatoa, in 1883 killed more than 36,000 people in a series of tsunamis.

Anak Krakatau, which means child of Krakatau, is the island that emerged from the area once occupied by Krakatau, which was destroyed in 1883. It first appeared in 1927 and has been growing ever since.

Reuters