Be Prepared: Tsunami risk from Sooke to Sidney

Black Press Media takes a look at emergency preparedness in Greater Victoria in this special report

This is part three of a special eight-part report done by Black Press Media on emergency preparedness in Greater Victoria. Find the series online at vicnews.com/tag/greater-victoria-emergency-preparedness

When a tsunami strikes will you be ready?

In March 2011, a 9.1 magnitude earthquake near Japan triggered a tsunami with waves that surged to heights of up to 130 feet (40 metres). It killed nearly 20,000 people and caused a major nuclear meltdown. This event is similar to what can be expected from the Cascadia Subduction Zone, which stretches from northern California to northern Vancouver Island, according to Washington State’s emergency management division.

READ MORE: Be prepared emergency series

But unlike some areas in Washington, “we don’t face the open ocean … we’re somewhat sheltered,” explained Geoff Amy, Colwood’s emergency program coordinator. “The threat varies from area to area … We do not, according to the scientists, have a threat or a major threat from a distant earthquake.”

The 2011 earthquake near Japan resulted in 15-centimetres waves in Colwood, with the most noticeable changes being to ocean currents, Amy said.

There are two types of tsunamis that could strike the region – local and distant. A local tsunami is associated with a ‘felt’ earthquake and a distant tsunami will originate far away and the earthquake may not be felt.

A tsunami is a series of long waves caused by a sudden shift in water triggered by an event such as an earthquake, landslide, volcanic eruption or explosion. The speed in which a tsunami travels is dependent on the depth of water. In deep oceans, a tsunami is barely noticeable but can travel at speeds upwards of 800 kilometres per hour. The closer it gets to shore, the higher the waves get and they begin to slow to speeds of 30 to 50 km/h.

Different coastal and offshore geographical features such as beach slope, reefs, bays and river mouths can also impact tsunamis, making them small and non-destructive in one area but potentially devastating short distances away.

The first wave may not the be largest or most damaging in the series and the time between them can vary from five minutes to two hours. In many parts of Japan, the fifth wave was the largest during the 2011 tsunami. Flooding and dangerous currents can also last for several hours or days, which is why residents are not advised to return to low lying areas until officials have determined it is safe.

But in 2018, a 7.9 magnitude earthquake in Alaska did trigger a tsunami warning for Greater Victoria, much to the surprise of local emergency programs coordinators.

In 2013, the Capital Regional District (CRD) conducted tsunami modelling, but it was based on an almost worst-case scenario, explained Tanya Patterson, the City of Victoria’s emergency program coordinator. Teams are working to update the modelling to include lesser threats, such as the 2018 earthquake which was believed and proven to be of minimal risk to Greater Victoria.

READ MORE: Tsunami warning ended for Greater Victoria

During the 2018 warning, 276 911 calls were made locally “and that was in the middle of the night,” said Sarah Hunn, Victoria’s emergency management community liaison. “People were calling 911 to ask about the tsunami … it’s not a means to get information,” she emphasised. “We see in other disasters the 911 system get overloaded and crash.”

Which means people in life and death situations cannot get the help they need.

Many residents also jumped into their vehicles and fled to higher ground, whether that was the top of a local mountain or the Malahat.

“People weren’t identifying what high ground was,” Amy explained. “You don’t need to go very far up Lagoon Road [in Colwood].”

A sentiment echoed by Patterson. “The public’s understanding of our risk wasn’t there and that’s what we’ve been working on.”

In the event of a magnitude 9 earthquake along the Cascadia Subduction Zone, the CRD predicts a tsunami will reach Port Renfrew in approximately 35 minutes with wave heights of up to 11.5 feet (3.5 metres), followed by Sooke Harbour within 60 minutes with waves of over eight feet (2.5 metres) and the Esquimalt and Victoria harbours in 76 minutes with respective wave heights of nearly nine feet (2.7 metres) and eight feet (2.5 metres). It will then reach Cadboro Bay within 90 minutes and Sidney within 110 minutes, with both expected to see waves up to 6.6 feet (two metres).

The CRD considers four metres – 13 feet above sea level – to be a safe distance.

During the 2018 warning, Amy reiterated emergency personnel had good plans in place – and it was a chance to practice in the middle of the night as the call came in around 2 a.m. Emergency personnel went door-to-door evacuating residences that could be impacted.

Amy noted residents looking for more information should go to their municipality’s website or attend an emergency preparedness seminar. Different areas also offer alert systems for residents to subscribe to. For example, Colwood, Langford, View Royal and Highlands have partnered on a system called Westshore Alert.

After the 2018 warning, the City of Victoria’s alert system went from approximately 6,000 subscribers to 60,000 within a week.

READ MORE: New videos highlight southern Vancouver Island’s tsunami risk

British Columbia’s tsunami notification zones

Five tsunami notification zones divide B.C.’s coastal communities. Three of the five apply to areas within the Capital Region.

Zone C is the outer west coast of Vancouver Island, including Port Renfrew (each zone includes all islands and inlets within it).

Zone D is the Juan de Fuca Strait from Jordan River to Greater Victoria, including the Saanich Peninsula.

Zone E is the Strait of Georgia including the Gulf Islands.

When tsunami warnings, watches or advisories are issued, the may make reference to these zones so it is important to know if you fall within one.

Pick up your Be Ready guide at Black Press newspaper offices or find it online at vicnews.com/e-editions.

katie.e@blackpress.ca


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