JMA Confirms No Tsunami Threat to Japan Following Indonesian Volcanic Eruption and Hokkaido Earthquakes on August 2, 2025

On August 2, 2025, the Japan Meteorological Agency (JMA) successively announced that there was no concern for tsunamis reaching Japan following a large-scale volcanic eruption in Indonesia and earthquakes off Nemuro and Kushiro in Hokkaido that occurred on the same day.

Indonesia Volcanic Eruption: Tsunami Concerns Dispelled

Following a large-scale volcanic eruption in Indonesia, concerns about a tsunami temporarily spread across Japan. However, the Japan Meteorological Agency (JMA) announced, based on prompt observation and analysis, that there would be no tsunami impact on Japan from this eruption. While it is possible for atmospheric pressure waves caused by volcanic eruptions to affect the sea surface and generate tsunamis, no such phenomenon was observed with this particular eruption. In response to this quick report, numerous messages of relief were posted on social media, such as 'Thank you for the breaking news, so relieved there's no tsunami concern!' and 'What good news!' Some also expressed concern about increased activity in the Pacific Ring of Fire.

Earthquakes Off Hokkaido: No Tsunami Threat

On the same day, multiple earthquakes also occurred off the coast of Hokkaido. An earthquake with a magnitude of 4.6 was observed off the southeast of Nemuro Peninsula, and another with a magnitude of 5.6 off Kushiro, both recording a seismic intensity of 3 in Hokkaido. For these earthquakes as well, the JMA promptly announced that there was 'no concern for a tsunami.' Local residents and related parties were relieved that there was no tsunami threat. Some voices pointed to a possible connection with recent large-scale seismic activity in the Kamchatka Peninsula, indicating that continued vigilance is necessary.

The JMA's swift provision of information has greatly contributed to alleviating public anxiety. Amidst a succession of natural disasters, the importance of promptly issuing accurate information has once again been highlighted.

The context

The Japan Meteorological Agency (JMA) is the primary government agency in Japan responsible for providing weather forecasts, earthquake information, and tsunami warnings. Its swift communication is crucial for public safety in a country frequently affected by natural disasters.

Indonesia, located in Southeast Asia, is part of the Pacific Ring of Fire, an area known for high seismic and volcanic activity. Japan, also situated on the Pacific Ring of Fire, is highly susceptible to earthquakes and tsunamis, making the monitoring of distant seismic and volcanic events critical. Hokkaido is Japan's northernmost main island, and the areas mentioned, Nemuro and Kushiro, are located on its eastern coast, facing the Pacific Ocean.

A unique aspect of volcanic eruptions is their potential to generate tsunamis not directly by displacing water, but through atmospheric pressure waves that travel across the ocean surface and can cause sea-level disturbances. The JMA's rapid analysis confirmed that this specific mechanism did not lead to a tsunami for Japan in the case of the Indonesian eruption. Earthquakes in Japan are measured using the Japan Meteorological Agency (JMA) seismic intensity scale, known as the 'Shindo' scale, which indicates the degree of shaking at a specific location, unlike magnitude which measures the total energy released.