New Land Emerges Near Anak Krakatau

Two new landmasses suddenly appeared around Mount Anak Krakatau. These small island mounds are suspected to be deposits left behind after the eruption of 4-6 September 2026. Further research is needed to confirm this.

Based on Sentinel satellite imagery, the small island mounds emerged roughly 760 meters to the northwest and 495 meters to the southeast of Mount Anak Krakatau. However, further research is needed to determine whether these landmasses are deposits or a new eruption center.

"If the results of field evaluation and verification confirm that volcanic material truly did emerge at both locations, this finding will help the Geological Agency understand the eruption process taking place and the shift in location of where volcanic material is being released," Lana said, as quoted by Tempo, Friday (2/10/2026).

The eruption in early September also added 32.8 hectares to Anak Krakatau's landmass. Previously, in August 2026, Sentinel satellite imagery showed Anak Krakatau's land area at 312.3 hectares.

Prof. Dr. Kuswaji Dwi Priyono, M.Si., Professor of Geography at Universitas Muhammadiyah Surakarta (UMS), said the appearance of new land at Mount Anak Krakatau is tied to the volcano's broader geomorphological cycle.

The emergence of the two island mounds, which netizens have dubbed "Krakatau's grandchild," is strongly suspected to be deposits left over from the 4-6 September 2026 eruption. According to Kuswaji, this can be understood by looking at how Mount Anak Krakatau has formed since its earliest appearance up to now.

"Volcanic material then continuously piled up on the seabed and formed these two mounds," Kuswaji said when interviewed on Friday.

While the preliminary assumption is that these are eruption deposits, further research is needed to determine whether the island mounds have a magma channel leading directly to the magma chamber through a new, separate fissure independent of the main chamber. Further analysis also needs to answer whether the island mounds show signs of magmatic activity, such as releasing magma and gas. Another indicator of magmatic activity would be local volcanic earthquakes occurring at the two mounds.

Given that Krakatau's caldera is relatively shallow, repeated eruptions accumulate over time, increasing the volume, building up the slopes, pushing the coastline further out to sea, and raising the mountain's height. "Magma from within the earth rises through a channel and emerges as lava. It then builds up and becomes the body of a new volcano," he explained.

The sun hadn't yet climbed very high on 27 August 1883 when Mount Krakatau began to show its force. In several stages, the 814-meter mountain started spewing out its contents through three craters: Danan, Perboewatan, and Rakata.

As the story goes, the massive blast occurred at 10:02 and could be heard as far as Perth, Australia, 3,110 kilometers away. The strength of Krakatau's eruption is estimated to be equivalent to 200 megatons of TNT, four times more powerful than the world's strongest bomb, Tsar Bomba.

The 1883 eruption destroyed 60 percent of Krakatau's body, leaving behind three islands. Spread across that caldera today are Sertung Island, Panjang Island, and Rakata Island. Krakatau's collapse triggered a tsunami that swept through Lampung and Banten, wiping hundreds of villages off the map and killing 36,417 people.

For more than four decades, Krakatau's caldera showed no signs of volcanic activity. From late 1927 into early 1928, volcanic activity began emerging from within the sea at Krakatau's caldera. Piles of volcanic material started appearing above the sea surface throughout 1928-1930, though they were frequently eroded away by waves. Anak Krakatau only truly formed into a permanent island in 1930.

Anak Krakatau has continued to erupt periodically, "growing" 7-9 meters every year. By 2018, its height had reached 338 meters above sea level.

Mount Anak Krakatau isn't the only mountain "growing" in the middle of the sea. Several other volcanoes have been recorded forming at sea and building up into islands, including Mount Hunga Tonga in Tonga, Surtsey Island in Iceland, Mauna Loa and Kilauea in Hawaii, United States, and the Canary Islands in Spain.

The Anak Krakatau phenomenon, he said, shows us how volcanic processes build islands up from the seafloor. A similar process once took place millions of years ago in the mountain range south of Java Island. One trace of it can still be seen at Nglanggeran Ancient Volcano, located in Gunungkidul Regency, Yogyakarta.

Mount Anak Krakatau has gone through a series of eruptions since July 2018. A major eruption occurred on 22 December 2018, causing part of Anak Krakatau's body to collapse, triggering a tsunami that swept across the coast of Banten. A total of 426 people were recorded killed in that event.

Professor Kuswaji Dwi Priyono explained that Mount Anak Krakatau is a stratovolcano, or cone-shaped volcano, with a Strombolian eruption type. "Its eruptions are usually explosively intense. The blasts are strong and happen repeatedly, periodically," Kuswaji said.

In 2018, the collapse of Anak Krakatau's slope caused the mountain to produce a Surtseyan-type eruption. This kind of eruption occurs from the interaction between magma and lake or sea water. The slope collapse created a new magma pathway toward the sea, one that had previously been directed toward the mountain's peak.

Mount Anak Krakatau produced a Strombolian eruption again during the 4-6 September 2026 eruption. This latest eruption produced a volcanic ash column 15,000 meters high, along with bursts of glowing lava.

The ejected lava then met seawater, triggering a cooling and solidification process. This is what caused Mount Anak Krakatau to grow in both height and surface area.

However, other factors, such as the dynamics of the Sunda Strait, can also affect Anak Krakatau's growth process. Kuswaji likened it to continuously piling up wet sand: the higher and steeper it gets, the greater the load becomes, and the lower its stability.

"If a slope failure occurs, part of Anak Krakatau's body could collapse into the sea and trigger a tsunami," he continued.

Kuswaji viewed Anak Krakatau as a living geomorphology laboratory. The ongoing series of eruptions represents a dynamic geomorphological process, seeking balance between the constructive forces of volcanism and the destructive forces of landslides and rockfalls.

Writer: Gede Arga Adrian

Translator: Farizal Luqman Majid

Editor: Al Habiib Josy Asheva