Born from the Caldera
After the catastrophic 1883 eruption obliterated most of the original Krakatau island, the area was quiet for decades — but not forever. Beginning in 1927, fishermen and researchers noticed something remarkable: a new volcanic island was emerging from the sea within the sunken caldera. They named it Anak Krakatau, meaning "Child of Krakatau" in Indonesian.
The island grew episodically through the twentieth century, driven by repeated eruptions that built up layers of lava and ash. By the early 21st century, Anak Krakatau had risen to over 300 metres above sea level and had become one of Indonesia's most closely watched volcanoes.
A Restless Volcano
Anak Krakatau is characterised by near-continuous low-level activity interspersed with more vigorous eruptive episodes. Its activity is predominantly Strombolian in style — rhythmic bursts of lava fragments and ash from the summit crater, often accompanied by glowing lava flows. This type of activity made it a popular destination for volcanology tourists willing to take a boat out from the Java or Sumatra coast.
However, the volcano's outwardly spectacular but seemingly manageable behaviour masked a structural instability that would have catastrophic consequences.
The 2018 Collapse: A Sudden Catastrophe
On the evening of December 22, 2018, during a period of heightened eruptive activity, a large section of Anak Krakatau's southwestern flank gave way. The collapse was rapid and massive — satellite data and bathymetric surveys later revealed that roughly two-thirds of the island's above-sea-level volume had disappeared.
The collapsing material — millions of cubic metres of volcanic rock and ash — plunged into the shallow waters of the Sunda Strait and generated a volcanic tsunami. Because the tsunami was triggered by a landslide rather than an earthquake, standard earthquake-based early warning systems did not detect it. The waves struck the coastlines of Banten Province in Java and Lampung Province in Sumatra with almost no warning.
Impact and Loss of Life
The tsunami waves reached heights of several metres along the affected coastlines. Hundreds of people were killed and thousands more were displaced. Coastal towns, beach resorts, and fishing villages bore the brunt of the damage. The disaster occurred on the evening of a weekend in December, when many areas were crowded with visitors.
What the Collapse Revealed
In the aftermath, Anak Krakatau was dramatically smaller. Satellite imagery showed the southwestern portion of the island had largely vanished. The collapse also exposed new pathways for seawater to interact with the magma system, triggering a new phase of intense phreatomagmatic eruptions in early 2019 as the sea flooded the vent.
Rebuilding Again
True to its nature, Anak Krakatau has continued to erupt and rebuild since 2018. By the early 2020s, new lava flows and eruption deposits had begun to restore the island's elevation. The cycle of growth, eruption, and collapse that has characterised this volcano since its birth continues — a vivid reminder of how dynamic and unpredictable this corner of the Earth remains.
Key Facts About Anak Krakatau
- First emerged: 1927
- Location: Within the 1883 caldera, Sunda Strait, Indonesia
- Eruption style: Predominantly Strombolian; occasional Vulcanian and phreatomagmatic episodes
- 2018 collapse: Triggered a deadly tsunami with minimal warning
- Current status: Actively growing and periodically erupting