A mountain steeped in one of Japan's darkest geological memories has once again given way. A magnitude 7.1 earthquake that hit southern Japan on Tuesday afternoon set off a partial collapse of Mayuyama in Shimabara, Nagasaki — a peak whose catastrophic failure over two centuries ago remains the deadliest volcanic-related event in Japanese history.
The Japan Meteorological Agency (JMA) placed the quake's epicenter roughly five kilometers east of Uto City, at a depth of about 10 kilometers, with the event occurring at 4:27 p.m. local time (3:27 p.m. Philippine time). The United States Geological Survey independently assessed the earthquake at a slightly lower magnitude of 6.8.
Maximum Shaking Registered in Uki City and Hikawa Town
According to the JMA, a seismic intensity of 7 — the ceiling of Japan's shindo measurement scale — was recorded in Uki City and Hikawa Town. This level of shaking is severe enough to bring down reinforced structures, render walking impossible, and produce cascading infrastructure failures across a wide area.
Prime Minister Sanae Takaichi confirmed that the quake had caused injuries, fires, power failures, structural collapses, and damage to road and bridge networks throughout the affected zone.
Shimabara's Iconic Mountain Fails on Camera
Monitoring camera footage reviewed by Shimabara City confirmed that the eastern slope of Mayuyama — the side facing the city — partially gave way shortly after the shaking began, Nagasaki broadcasters KTN and NBC reported. Firefighters witnessed the collapse as it unfolded, and video captured by residents showed debris cascading down the mountain in dense white clouds while emergency warnings blared across the city.
As of Tuesday evening, no casualties from the slope failure had been reported. Nagasaki Prefecture dispatched a disaster helicopter at 5:12 p.m. to conduct aerial surveys of Mayuyama. Officials also confirmed that no abnormality was detected at the Fugendake lava dome on the nearby Mount Unzen.
Slope Had Already Been Weakened Before Tuesday
Tuesday's collapse did not occur without warning. Shimabara City had already been monitoring Mayuyama's condition after surface peeling was recorded on the mountain following a strong earthquake in April. That deterioration was further compounded by heavy rainfall in June, which expanded the existing damage and prompted inspections by mountain specialists.
The 7.1-magnitude event appears to have pushed the already-compromised slope past a critical breaking point, though authorities are still evaluating the full extent of what failed.
More Than 150,000 Residents Ordered to Evacuate
According to Prime Minister Takaichi's office, more than 150,000 people were ordered to move to designated evacuation centers in the wake of the earthquake. Approximately 40,000 households lost power across the affected area.
NHK footage broadcast after the disaster showed structures on fire, collapsed buildings, large fractures in an elevated highway, and a derailed freight train. Expressway overpasses in Yatsushiro sustained major damage, and part of a bridge in that city also collapsed. Chipmaker TSMC evacuated employees from its nearby plant, while Sony announced it was assessing its facilities for potential damage.
Tsunami Alert Raised and Lowered; Shelters Opened Across the Region
A tsunami warning of up to one meter was issued for the Ariake and Yatsushiro Seas in the immediate aftermath of the quake, though it was later lifted. In Nagasaki Prefecture, Minamishimabara recorded a seismic intensity of 5-strong, issued a Level 4 evacuation order, and activated eight emergency shelters. Shimabara City opened seven additional shelters to accommodate displaced residents.
JR Kyushu suspended conventional rail services and halted operations on the Nishi-Kyushu Shinkansen line in response to the disaster.
The 1792 Catastrophe That Tuesday's Event Recalled
The historical weight of Tuesday's collapse cannot be overstated. In May 1792, earthquakes connected to an eruption of Mount Unzen caused Mayuyama's flank to collapse into the Ariake Sea, generating a devastating tsunami that swept into present-day Kumamoto. The event killed an estimated 15,000 people on both coastlines and is still remembered in Japan through the phrase "Shimabara erupted, Higo affected." It remains the deadliest volcanic disaster in Japanese recorded history.
Tuesday's earthquake inverted that historical geography in a striking way: instead of a Shimabara-side eruption destabilising the mountain and sending a wave toward Kumamoto, it was a Kumamoto-side earthquake that shook the very same peak across the bay.
JMA Links Epicenter to Region Near 2016 Hinagu Fault
The JMA noted that Tuesday's epicenter is located approximately 20 kilometers from the Hinagu fault zone, the same seismic structure responsible for the April 2016 Kumamoto earthquakes, which killed more than 270 people. However, the agency said it was premature to draw a direct connection between Tuesday's event and that earlier seismic sequence.
The JMA also warned residents throughout the region to remain alert for powerful aftershocks and an elevated risk of landslides for approximately one week following the main shock.
By the Numbers
- 7.1 — magnitude of the earthquake as measured by the JMA
- 6.8 — independent magnitude reading from the United States Geological Survey
- 7 — maximum seismic intensity recorded, the highest level on Japan's shindo scale, in Uki City and Hikawa Town
- ~10 km — depth of the earthquake's epicenter below the surface
- 150,000+ — residents ordered to evacuate to emergency centers
- ~40,000 — households that lost electrical power
- ~15,000 — people killed in the 1792 Mayuyama collapse and resulting tsunami
- 270+ — deaths attributed to the 2016 Kumamoto earthquakes near the Hinagu fault zone
- ~20 km — distance between Tuesday's epicenter and the Hinagu fault zone
- 5:12 p.m. — time Nagasaki Prefecture launched a disaster helicopter to survey Mayuyama from the air
Why This Matters
Tuesday's earthquake ranks among the most powerful to strike the Kumamoto area since the catastrophic 2016 sequence, generating Japan's maximum recorded shaking intensity and forcing mass evacuations of more than 150,000 people. The partial collapse of Mayuyama — a slope already documented as unstable following earlier seismic activity and June rainfall — raises urgent questions about what remains of the mountainside, with the JMA warning of continued landslide risk for up to a week. The event further highlights the enduring seismic danger across Kyushu, where historically active fault systems lie beneath densely populated cities and major industrial facilities, including plants operated by global companies such as TSMC and Sony.
Source: breakingnewsnegor.com / wire reports