Eruptions imminent, subsea quakes suggest

Swarms of mini-earthquakes along tectonic plates five kilometres underwater on the Pacific Ocean floor off the coast of Vancouver Island have caught the attention of ocean scientists.

Not because the earthquakes, up to 200 per hour at their peak on March 6, signal any kind of impending seismic catastrophe, but because they point to an “impending magmatic rupture” on the Juan de Fuca Ridge, 240 kilometres from Vancouver Island.

The volcanic eruption, at a location known as the Endeavour hydrothermal vents, will see tectonic plates crack open and magma rise to fill the expanding ocean floor. Scientists will be able to record it happening in real time.

The event differs from subduction zones, which form when plates collide and are the source of damaging earthquakes on land.

“This is about scientific discovery, so it's always very exciting for us when we have infrastructure in place that delivers real-time data so that we can better understand what's going on at these very dynamic locations on the ocean floor,” said Kate Moran, CEO of Ocean Networks Canada.

ONC is the University of Victoria research entity that operates the NEPTUNE (North-East-Pacific Time-Series Undersea Networked Experiments) Observatory, an 800-km loop of fibre-optic cable that connects sensors on the ocean bottom at crucial locations, such as the Endeavour vents.

Moran said seismic activity happens all the time along tectonic plates, and such ruptures happen along the Juan de Fuca Ridge in cycles of about 20 years, so an impending event this year isn't unexpected.

Researchers have witnessed an increase in seismic activity at the Endeavour vents since 2018, but it has increased in frequency, including a quake measured at 4.1 on the Richter scale that rattled Vancouver Island on Wednesday.

“(That) caught my attention,” Moran said of the swarms of quakes being recorded.

The difference from the last such magmatic event in 2005, however, is that it will be the first to occur since the NEPTUNE observatory was completed in 2009, which will let researchers watch the activity as it is happening rather than collecting from sensors after the fact.

Moran said some researchers describe the rifts where the Earth's plates spread as looking a little like “seams on a baseball.”

“But they're almost all under the ocean, so understanding these processes are really important,” Moran said. “We need to understand the cycle of ocean crust formation and then the cycle of the subsequent subduction earthquakes. So it's fundamental.”

The rupture, when it happens, will be similar to the volcanic eruptions that have happened recently in Iceland, but not nearly as dramatic, said ocean seismology PhD candidate Zoe Krauss.

“Iceland is kind of also on a midocean ridge, so they're not these explosive types of events,” Krauss said. “It is more effusive and erupts in a line, if you will.”

However, Krauss said researchers don't expect to see magma break through the surface along the Endeavour vents off Vancouver Island.

Krauss said past observations show that at the Endeavour vents, ruptures happen when the spread of plates reaches about a metre.

“What the magma does is essentially intrudes and fills those cracks,” Krauss said. “And then it cools and it forms that new ocean crust.”

A magmatic rupture would mark a culmination of PhD studies Krauss embarked on at the University of Washington five years ago, “and it's so cool.”

The NEPTUNE observatory gives researchers a long-term view of seismic activity along a midocean ridge, which is context that a lot of other researchers don't get, Krauss said.

“We can see everything that led up to it, we can see the changes that led up to it, and that is really, really rare for a sea floor setting,” she added.

Moran said that toward the end of June, OCN will send a vessel with a remotely operated submersible with cameras to look at what has happened and better pinpoint where it is.

She added that researchers can't predict when such events will happen, but they are lucky that they can marvel at the intricacies of the seismic activity as it happens.

Moran said the seismometers included among NEPTUNE's sensors are so sensitive they can hear the sounds of fin whales communicate among one another, as well as the rumblings of the Earth.

“In the past, we've actually observed (that) you can hear fin whales talking, or whatever you want to call it, and then you can hear an earthquake happen and (whales) stopped talking to listen to the earthquake,” Moran said.

“Then they start talking again. So it's really cool.”