The 1883 eruption of Krakatoa was one of the most violent volcanic events in recorded history. It obliterated roughly two-thirds of the island's mass, collapsing the peaks of Perboewatan and Danan and leaving only the southern half -- the Rakata volcano -- as a remnant above water. The lost landmass became a shallow submarine caldera, and for decades nothing visible occupied it. Then, in early 1927, volcanic activity began stirring between the sites where Perboewatan and Danan had once stood. The new island's growth was not a steady ascent but a stuttering argument between creation and erasure, with the sea winning round after round until the volcano's output finally exceeded what the waves could tear down. Once permanently established, Anak Krakatau grew at a remarkable pace: its summit rose by an average of 7 to 9 meters per year through September 2018.

Scientists knew what was coming. In January 2012, volcanologists at the University of Oregon published a warning that a tsunami caused by flank collapse of Anak Krakatau was likely. The volcano had been building itself on the steep eastern slope of the 1883 caldera, an inherently unstable foundation. They identified the western flank as the section most likely to fail. Six years later, on 22 December 2018, after months of escalating eruptions -- Strombolian bursts in October had been lobbing lava bombs into the surrounding water -- the southwest sector of the volcano, including the summit, collapsed into the sea. The resulting tsunami sent waves up to five meters high crashing into more than 300 kilometers of coastline across Sumatra and Java. The disaster agency's final count: 437 dead, 14,059 injured, 40,000 displaced. It was the second deadliest volcanic eruption of the 21st century.

Satellite data and helicopter footage confirmed the scale of the destruction within a day. The volcano had lost over two-thirds of its volume. Its elevation above sea level had plummeted dramatically. The main volcanic conduit was now erupting from underwater, producing Surtseyan-style explosions -- columns of steam and ash blasting upward where the crater met the sea. The spectacle was terrible and fascinating in equal measure. By 10 January 2019, satellite radar showed the volcano was already rebuilding. The crater, which had been ripped open to the ocean during the collapse, had reformed a complete rim above sea level. By May 2019, phreatomagmatic eruptions were reshaping the newly reconstructed crater as Anak Krakatau steadily regained height, filling in the scars of December with fresh volcanic material.

On the morning of 10 April 2020, residents of Jakarta -- 150 kilometers away -- heard a deep rumble. Anak Krakatau was erupting again. The initial burst lasted just one minute and twelve seconds, but it threw an ash column 200 meters into the air, with secondary plumes reaching 11 to 14 kilometers in altitude. Lava fountains lit the night sky. The eruption was largely magmatic, and no widespread damage was reported. Twenty-one minor eruptions followed in early 2022, the largest on 24 April. A further eruption cycle began in September 2023. The pattern is relentless: eruption, growth, collapse, eruption. Anak Krakatau sits on the Pacific Ring of Fire, at a subduction zone where the Australian Plate grinds beneath the Sunda Plate. The geological engine driving the volcano is not going to stop. The only question is the scale of what comes next.

For volcanologists, Anak Krakatau is an extraordinary natural laboratory -- a young, active volcano whose entire life history has been observed and documented. From its first tentative emergence in 1927 through its catastrophic 2018 collapse and ongoing reconstruction, every phase has been studied. The island sits in the Sunda Strait between Java and Sumatra, visible from the western tip of Ujung Kulon National Park and surrounded by the remnant islands of the Krakatoa archipelago: Sertung, Panjang, and Rakata. Together they form a ring around the caldera, a geological family portrait spanning 140 years of destruction and renewal. The island is uninhabited, but it is never unwatched.