Increased activity at Anak Krakatau volcano, Indonesia

Indonesia’s Anak Krakatau volcano experienced an increase in activity over the past 12 hours, resulting in four intense eruptions from late March 27 to early March 28, 2023.

The first notable eruption occurred at 21:12 UTC on March 27, with an ash column height of approximately 800 m (2 625 feet) above the peak or 957 m (3 140 feet) above sea level. The gray ash column had a thick intensity and was observed moving to the northeast. This eruption was recorded on a seismograph with a maximum amplitude of 60 mm and a duration of 145 seconds.¹

The second eruption took place at 00:43 UTC on March 28, producing an ash column that reached 2 000 m (6 562 feet) above the peak or 2 157 m (7 073 feet) above sea level. The black ash column, with thick intensity, also moved toward the northeast. The seismograph recorded a maximum amplitude of 65 mm and a duration of 118 seconds during this eruption.

The latest reported eruption took place at 05:21 UTC on March 28, with the ash column reaching a height of 2 500 m (8 202 feet) above the peak or 2 657 m (8 717 feet) above sea level. The black ash column, with thick intensity, was observed moving to the west. A seismograph recorded this eruption with a maximum amplitude of 74 mm and a duration of 146 seconds.

The fourth eruption took place at 08:13 UTC. The height of the eruption column was observed to be ± 1 500 m (4 921 feet) above the summit (± 1 657 m or 5 436 feet above sea level).

The ash column was observed to be gray to black with thick intensity to the west. The eruption was recorded on a seismograph with a maximum amplitude of 70 mm and a duration of 89 seconds.

The Aviation Color Code is at Orange and the Alert Level remains at 3 (on a scale of 1-4).

The public is urged to stay at least 5 km (3.1 miles) away from the crater.

Geological summary

The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. The collapse of the ancestral Krakatau edifice, perhaps in 416 CE, formed a 7 km (4.3 miles) wide caldera.

Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan volcanoes and left only a remnant of Rakata volcano.

This eruption, the 2^nd largest in Indonesia during historical time, caused more than 36 000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km (25 miles) across the Sunda Strait and reached the Sumatra coast.

After a quiescence of less than a half-century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.²

References:

¹ Anak Krakatau volcano updates – PVMBG – March 27 and 28, 2023

² Anak Krakatau – Geological summary – GVP

Featured image credit: PVMBG