Weekly Volcanic Activity Report: August 27 - September 2, 2025
This report summarizes volcanic activity observed between August 27th and September 2nd, 2025, based on data from the Smithsonian Institution / US Geological Survey’s Global Volcanism Programme (GVP). The report, managed by Sally Sennert, details activity at Suwanosejima, Japan, and Yasur, Vanuatu.
Suwanosejima, Japan
Activity at Suwanosejima continued during the reporting period. On August 29th, an explosion generated a plume that rose above the crater rim, reaching 1.8 km above the crater rim and drifting north. Minor ashfall was reported in Toshima Village, located 3.5 km SSW of the volcano. The Alert Level remained at 2 (on a five-level scale),and the public was advised to exercise caution within 1.5 km of the crater.
Suwanosejima is an 8-km-long andesitic stratovolcano in the northern Ryukyu Islands, characterized by two active summit craters. The summit features a large breached crater extending to the sea on the eastern flank, formed by a past edifice collapse. Historically, the volcano exhibited intermittent Strombolian activity from the Otake, NE summit crater, between 1949 and 1996, with periods of inactivity lengthening in recent decades. The largest recorded eruption occurred in 1813-14, producing thick scoria deposits and lava flows reaching the western coast. this eruption caused the summit of Otake to collapse, creating a debris avalanche and a large scarp extending to the eastern coast, leading to the island being uninhabited for approximately 70 years. Lava flows also reached the eastern coast in 1884. Currently, approximately 50 people reside on the island.
Yasur, Vanuatu
The Vanuatu meteorology and Geohazards Department (VMGD) reported that Yasur remained at a “major unrest” level, corresponding to Alert Level 2 (on a scale of 0-5) throughout August. Observations, including field photos and webcam images, confirmed continued explosions producing emissions of gas, steam, and/or ash on August 1-17, 20-23, and 25-28. Satellite imagery detected sulfur dioxide gas emissions during august 1-4, 6-14, 16-19, and 22-27, while low-level thermal anomalies were identified during August 3-7, 10-13, 21, and 25-26. Seismic data corroborated ongoing volcanic activity with occasionally strong explosions.
The VMGD warned that ejected material from explosions could fall within and around the crater and reminded the public to avoid entering the restricted area within 600 m around the boundaries of the Permanent Exclusion Zone, designated as Danger Zone A on the hazard map.
Yasur, located at the SE tip of tanna Island, is a pyroclastic cone with a nearly circular, 400-m-wide summit crater. It has exhibited essentially continuous Strombolian and Vulcanian activity since at least 1774, potentially for the past 800 years. The active cone is contained within the Yenkahe caldera and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst, where Yasur is located, lies within the siwi ring fracture, associated with the eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst has raised Port Resolution harbor more than 20 m during the past century.
