Two huge sinkholes have formed in the Greater Toronto Area in the past week causing transit delays and gridlock, and leaving many residents wondering, what causes them?
On Friday morning, a large sinkhole formed at the intersection of Yonge and Melinda Streets in the city’s Financial District.
According to a City of Toronto spokesperson, staff have secured the area and are investigating the cause of the phenomenon and determining which repairs need to be made.
“We understand this disruption affects people who live and work in the area, and we thank those impacted for their patience as we work to restore the road as quickly and safely as possible,” the spokesperson told Now Toronto in an email statement.
As a result of the issue, TTC has announced service disruptions in the area, with its eastbound 504C and 504D replacement buses having to detour via King St. W., Adelaide St. E. and Jarvis St.
As of 3:29 PM – 504 King: Detour eastbound via King St W, Toronto St, Adelaide St E and Jarvis St due to emergency sinkhole repairs. https://t.co/i3JXdmlPtc
— TTC Service Alerts (@TTCnotices) July 11, 2025
The affected replacement buses are part of major streetcar route changes, which the TTC announced back in May due to construction at the intersection of King and Church streets.
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According to the city, there is still no timeline for when the sinkhole repairs will be completed.
This has not been the only sinkhole in the region this week. On Tuesday, a large sinkhole also appeared in Brampton, shutting down all eastbound lanes on Steeles Ave. from Airport Rd. to Goreway Dr.
WHAT ARE SINKHOLES AND HOW DO THEY APPEAR?
Engineering expert and Postdoctoral Fellow at the University of Toronto Dr. Peter Adesina, explains that sinkholes are holes created under the soil, which eventually cause the ground above it to collapse.
The expert says the phenomenon can happen anywhere where the soil under the ground is weakened, which can be triggered by many different factors. One reason could be human action that messes with the soil, including drilling, excavating, mining or more.
“Mining is essentially the removal of mineral resources from the ground. So, that process of removing material from the ground can weaken the soil adjacent to where the mining is going on, and when the soil is weakened, that soil could actually flow out of its place. So, you have the collapse of the ground above, and then you see a sinkhole happening as a result,” he told Now Toronto.
Another way a sinkhole can be formed is by the presence of water underground.
For instance, if a water pipe buried underground bursts or leaks, it could wash off the soil, which could eventually also lead to a sinkhole appearing.
The phenomenon can happen naturally through underground sources of water, which could lead to something called internal erosion, for example.
“The soil typically will be composed of bigger particles and smaller particles. So then, if you have water flow against the soil, the finer particles can then be moved with the water. So, when it gets removed, then you’ll be left with the bigger particles and voids between them,” he added.
Adesina says that in order to fix a sinkhole, experts need to conduct a thorough investigation of its causes, which could happen over different periods depending on the conditions.
“If you don’t understand the cause of the sinkhole, you can actually place soil back into the hole that has been created, and then you go away. And within like, maybe a month or two, you can have the sinkhole reoccurring,” he added.
In order to fix it, experts can choose different methods to strengthen the soil, including compacting the soil and using strong materials to fill in the hole.
Additionally, Adesina advises Torontonians to stay cautious and avoid going near the sinkhole, as depending on the cause and extension of the issue, the soil around it could be unstable and eventually also collapse.
“The location of a sinkhole is not a sightseeing site…it’s a place where people have to get rid of and go away from,” he said. “You never can tell what the condition of the soil [is]… so people could actually get trapped into the sinkhole.”
