Dangerous caldera: One of the most explosive supervolcanoes on earth is replenishing fresh magma

A major volcanic system beneath the ocean has begun refilling with fresh magma, offering scientists a rare opportunity to study how some of Earth’s largest volcanoes recover after catastrophic eruptions. The caldera of Kikai, located off the southern coast of Japan, is one of the most explosive supervolcanoes on the planet, and recent findings suggest its deep magma reservoir is once again accumulating molten rock. The discovery was made by researchers from Kobe University, who have published their results in the journal Communications Earth & Environment. Their work provides new insights into the processes that allow such massive volcanic systems, like Yellowstone in the United States and Toba in Indonesia, to rebuild themselves over time. Understanding these mechanisms could help improve predictions of future large-scale eruptions, which remain difficult to forecast due to limited knowledge of the underlying geological activity. Kikai is a largely submerged caldera formed approximately 7,300 years ago by one of the largest known eruptions of the Holocene epoch, which began around 11,700 years ago. Calderas form when an eruption empties so much magma that the ground above the magma chamber collapses, creating a wide, relatively shallow depression instead of the typical conical shape of a volcano. The scale of such eruptions is hard to grasp; the volume of erupted material could cover New York's Central Park with a layer of lava up to 12 kilometers thick, according to reports from Science Daily. Yellowstone, Toba, and Kikai are among the best-known examples of large caldera-forming volcanoes. Scientists know these systems can erupt multiple times, yet the processes that enable them to accumulate vast quantities of magma remain poorly understood. This lack of understanding makes predicting their future behavior particularly challenging. Geophysicist Nobukazu Seama from Kobe University emphasized the importance of studying how such large volumes of magma can accumulate. “We must understand how such large amounts of magma can build up so we can comprehend how massive caldera eruptions occur,” he stated. The underwater location of Kikai presented both challenges and advantages for researchers. While the depth of the caldera might seem like an obstacle, it allowed for extensive and systematic investigation of the entire volcanic structure. Seama explained, “The underwater position enables us to conduct comprehensive studies of large-scale structures.” The research team from Kobe University collaborated with the Japan Agency for Marine-Earth Technology and Science (JAMSTEC) to investigate the crust beneath the caldera. They used arrays of air guns to generate controlled seismic impulses, while seismometers placed on the seabed recorded how these waves propagated through the rocks. By measuring changes in the speed and direction of seismic waves, scientists can create images of subsurface structures and identify areas that might contain partially melted rock. These techniques helped reveal a large area rich in magma directly beneath part of the Kikai caldera that had previously produced a massive eruption. The findings indicate that this magma chamber is part of the same underground system that supplied magma during the ancient eruption. However, evidence suggests that over time, new molten material has entered the reservoir, indicating ongoing geological activity rather than a static accumulation. Near the center of the Kikai caldera, a lava dome has been forming for roughly 3,900 years. Such domes develop when dense magma slowly rises toward the surface and accumulates around a volcanic vent, rather than flowing freely. Chemical analyses of materials from this dome and other more recent volcanic activities show differences from the magma expelled during the earlier, massive eruption. This suggests that the current magma is distinct and represents a new phase of activity within the system.