As Victoria’s coastline experiences some of its lowest tides in years, the receding water has exposed a slab of granite at Harling Point, the rocky beach beside the Chinese Cemetery in Oak Bay.
It’s no ordinary rock, according to Edwin Nissen, University of Victoria professor of ocean and earth sciences. It most likely travelled — via glacier — hundreds of kilometres from the Coast Mountains north of Vancouver between 10,000 and 20,000 years ago.
Nissen said the technical term is a glacial erratic — basically an out-of-place rock — in this case, an igneous rock from the mainland that’s been transported by glacial movement.
During the Pleistocene era, which ended roughly 12,000 years ago, enormous glaciers flowed down from the Coast Mountains, over Vancouver Island and out into the Pacific Ocean.
The constant flow of the glacier would have ripped up rocks and transported them in the ice, eventually depositing them randomly when the glacier melted, as the era of massive glaciers came to an end.
Igneous rocks, formed from magma, are not typically found on the coastline of Vancouver Island, Nissen said.
Here, there is volcanic rock formed on the sea floor and softer, metamorphic rocks formed from sediment, often closer to land.
The crystallized igneous rock isn’t the only reminder of historic glaciers along the region’s shorelines. Nissen notes that glacial striations — basically, scratch marks left by tough igneous rocks along the softer bedrock — reveal the north-south flow of the ice.
“When you have hard rock scraping over soft rock, the hard rock will produce these really deep-set grooves in the softer bedrock,” he said. “It’s not necessarily a low-tide thing — you can actually see them any time. But they might be more exposed by low tide.”
The markings are clues of a long-gone era, but relatively speaking, the geologic wonder displays only a blip in the Earth’s timeline, Nissen said.
“Twenty thousand years or 10,000 years ago, whenever these glaciers were flowing and retreating, is a blink of the eye in geological terms,” he said. “The earth is 4.5 billion years old and a lot of the rocks we see here are tens or hundreds of millions of years old.”
While visible at normal tides, the foreign rocks and glacial striations are revealed in full now because of an abnormally low tide, a phenomena caused by the high sun of summer solstice aligning with a full moon closest in its orbit to Earth, also called a moon in perigee.
The tide has retreated about 20 to 25 centimetres below an average low-tide line, said Richard Dewey, associate director of science at Ocean Networks Canada. The last full moon in June brought similarly low tides.
“They’re rare but not unexpected,” Dewey said. “They often come together this time of year and particularly during summer solstice.”
The phenomena also creates a long tidal cycle, he said.
“Often we think about high tide and low tide as being about six hours apart, but on Wednesday, we had one very low tide at mid-morning and high tides were at midnight.”
The next big low-tide event is expected mid-June 2026.
With the sun and moon exercising their full power over B.C.’s south coast, the usually underwater worlds of vegetation, shellfish, crabs and other intertidal species are also exposed to the sun. The adaptive seaside habitat is diverse and abundant, oscillating between exposure and submersion.
“This habitat that’s getting exposed at these really low tides really isn’t that far out of reach,” Dewey said. “It’s 30 to 40 metres out from shore on a sloping beach … It’s there all the time, but we get to see it in the air during these low tides.”
Dewey said the low tides are only a concern if they align with heat domes like the one that hit B.C. last summer and killed an estimated one billion inter-tidal animals in the Salish Sea.
“If we experience more heat domes, they will occur during summer solstice, when we see the lowest tides,” Dewey said. “The combination of those is something to watch for.”
Those who want to explore the glacial erratics or check out intertidal species during low tide should do so, but with caution, Dewey said.
“We want to be passive observers and not add extra stress to these systems that are experiencing these low tides,” he said. “The last thing they need is for us to come along and disturb them even further.
“Look and explore but try not to disturb.”
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