As Victoria’s coast experienced some of its lowest tides in years, the receding water exposed a granite slab at Harling Point, the rocky beach next to the Oak Bay Chinese Cemetery.
This is no ordinary rock, according to Edwin Nissen, professor of ocean and earth sciences at the University of Victoria. It most likely traveled – across a glacier – hundreds of kilometers from the Coast Mountains north of Vancouver between 10,000 and 20,000 years ago.
Nissen said the technical term is glacial erratic — basically misfit rock — in this case, igneous rock from the continent that was transported by glacial movement.
During the Pleistocene epoch, which ended about 12,000 years ago, huge glaciers descended from the Coast Mountains, over Vancouver Island, and into the Pacific Ocean.
The constant flow of the glacier would have torn the rocks apart and transported them into the ice, eventually depositing them randomly as the glacier melted as the massive ice age ended.
Igneous rocks formed by magma are not commonly found along the coast of Vancouver Island, Nissen said.
Here there is volcanic rock formed on the sea floor and softer, metamorphic rocks formed from sediments, often closer to land.
Crystallized igneous rock is not the only reminder of historic glaciers along the region’s coastline. Nissen notes that glacial striations—basically scratch marks left by tough igneous rocks on softer bedrock—reveal the flow of ice from north to south.
“When you scrape hard rock over soft rock, the hard rock will produce these really deep channels in the softer rock,” he said. “It’s not necessarily a low-tide thing — you can actually see them at any time.” But they may be more exposed to ebb.
The markings are clues to a long-gone era, but relatively speaking, the geological wonder represents only a moment in Earth’s timeline, Nissen said.
“Twenty thousand years ago or 10,000 years ago when these glaciers were flowing and retreating is the blink of an eye in geological terms,” he said. “The Earth is 4.5 billion years old, and many of the rocks we see here are tens or hundreds of millions of years old.”
Although visible at normal tides, the alien rocks and ice sheets are now fully exposed due to an unusually low tide, a phenomenon caused by the high summer solstice sun aligned with a full moon at its closest orbit to Earth. also called the moon at perigee.
The tide has receded about 20 to 25 centimeters below the mean low tide line, said Richard Dewey, associate director of science at Ocean Networks Canada. The last full moon in June brought similar ebbs.
“They’re rare, but they’re not unexpected,” Dewey said. “They often congregate at this time of year and especially during the summer solstice.”
The phenomenon also creates a long tidal cycle, he said.
“We often think of high tide as being about six hours apart, but on Wednesday we had one very high tide mid-morning and high tide at midnight.”
The next major tidal event is expected in mid-June 2026.
As the sun and moon exert their full power over the southern coast of British Columbia, the normally underwater worlds of vegetation, shellfish, crabs and other intertidal species are also exposed to the sun. Adaptive coastal habitat is diverse and abundant, varying between exposure and submergence.
“That habitat that’s exposed at these really low tides is really not that far out of reach,” Dewey said. “It’s 30 to 40 meters offshore on a sloping beach… It’s there all the time, but we can see it in the air during these low tides.”
Dewey said the tides are only a cause for concern if they match heat domes like the one that hit British Columbia last summer and killed an estimated one billion intertidal animals in the Salish Sea.
“If we experience more heat domes, they will occur during the summer solstice when we see the lowest tides,” Dewey said. “The combination of those is something to watch.”
Those who want to study glacial drifts or check out intertidal species at low tide should do so, but with caution, Dewey said.
“We want to be passive observers and not add additional stress to these systems that are experiencing these outflows,” he said. “The last thing they need is for us to come and disturb them even more.”
“Look and explore, but try not to disturb.”
ngrossman@timescolonist.com
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