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On Saturday, June 7, 2025, a large rock fragment unexpectedly broke off from Iyamopo Hill in Igbeti, a town in Olorunsogo Local Government Area of Oyo State, South West Nigeria.
A resident, Muneef Alawode, captured the event on video around 4:30 p.m. This video quickly spread on social media, with other Facebook users posting similar videos here and here.
This event raised questions and concerns about the cause of the rock breaking. Many Facebook users who commented on the video mistakenly identified the geological occurrence as a volcanic eruption. The incident was also widely reported by Oyo state-based news outlets here, here, here, and here.
Thankfully, no one was injured, and no buildings were damaged. But what caused this sudden break? To better understand this, DUBAWA spoke with experts who explained what happened at Iyamopo Hill in simple terms.
The incident was caused by weathering
A lecturer in the Geology department at the University of Ilorin, Dr. Idris Olaniyi, explained that what happened at Iyamopo Hill is most likely a result of a natural process called weathering.
He said that weathering is the process by which rocks slowly break down or change over time due to factors such as heat, rain, wind, and even the presence of plant roots.
“What happened is called physical weathering, particularly exfoliation. It’s very common in hot climates like Nigeria. Rocks expand and contract because of daily temperature changes. Over time, cracks form, and eventually, the rock breaks apart,” he said.
According to National Geographic Education, weathering is the breakdown or dissolution of rocks and minerals on the surface of Earth. Once a rock has been broken down, erosion transports the bits of rock and mineral away.
These processes carved landmarks such as the Grand Canyon in the U.S. state of Arizona. Several factors, including climate, rock type, surface area, and time, influence the rate of weathering.
In Nigeria’s hot and wet climate, rocks expand during the day when temperatures rise and contract at night when it cools down. Over time, this constant movement creates cracks inside the rock. Rainwater also seeps into the cracks, causing them to widen.
Dr. Yemi Adedeji, an Environmental Geoscientist based in Ibadan, said rocks expand during the day when temperatures rise and contract at night. He added that after months or years, a part of the rock may become loose and eventually fall off, just like what happened at Iyamopo Hill.
“This kind of break is common in hilly or mountainous areas, especially where the rocks are exposed to the sun and rain without cover.
“Many rocks in southwestern Nigeria, especially around Igbeti, are made up of marble and other minerals that respond to heat. If cracks already exist in the rock, heat and rainwater make the break faster,” he said.
A 2015 research paper published in the International Journal of Civil Engineering and Technology supports this explanation.
The study, “The Effects of Weathering on Some Physical and Mechanical Properties of Selected Carbonate Rocks in Southwestern Nigeria,” showed that rocks in Oyo and nearby areas break down over time due to a mix of temperature, rain, and pressure.
“This happened before,” the traditional ruler reacts
The Onigbeti of Igbeti, Oba Engr. Bashir Olamilekan Abioye Siyanbola IV confirmed that this is not the first time such an event has occurred.
“It happened last year too, in April 2024, though that time, it was not as large as this one,” the monarch said.
According to him, geologists who examined the earlier event explained that harsh sunlight and heat were the primary causes. “They told us that the constant sun led to expansion and breaking of the rock bonds,” he added.
He urged the public to stay calm but warned residents and tourists to avoid the base of the hill and other cracked areas for safety.
No evidence of an earthquake
The Nigeria Mining and Geosciences Society (NMGS) issued a statement, signed by its President, Rose Ndong. It made available to DUBAWA, clarifying that the event, characterised by audible rock cracking and movement, was a natural geomorphic process known as exfoliation. This process involves the peeling away of outer rock layers due to repeated heating and cooling cycles, a common phenomenon in granite terrains.
According to the NMGS, the intense heat from February 2025 to May 2025, followed by a sudden cooling phase, triggered this rock response, leading to minor vibrations that some residents mistook for seismic activity.
Experts from NMGS explain that the granite inselberg (a distinctive landform, an isolated rock hill or mountain that stands out from a surrounding plain) experienced internal stress due to temperature fluctuations. This stress caused the outer rock layers to expand and contract unevenly, leading to the formation of cracks and the eventual detachment of rock slabs.
While the vibrations may have felt unsettling, the NMGS stressed that there is no evidence of tectonic movement or an actual earthquake.
The agency said it has already dispatched a team of geoscientists to conduct further site assessments to better understand the occurrence and its implications for local safety.
As a precaution, the NMGS advises residents to evacuate houses and farmlands within 50 to 100 metres of the inselberg to avoid any danger from future rock falls. They also recommend a halt to physical development near the site.
Experts like Yemi believe that professionals should check the hill regularly to prevent future risks. The Oyo State Emergency Management Agency (OYSEMA) or the Nigerian Geological Survey Agency (NGSA) could assist in inspecting and monitoring the area.
He also advised that warning signs and safety barriers should be placed near parts of the hill with visible cracks. Community awareness campaigns can also help keep residents and visitors informed.
