Struck by a 125 Foot High Wave; Canada's Recent Tsunami

In the early afternoon of December 4, 2007, a serene day at Chehalis Lake turned catastrophic. A massive landslide triggered a tsunami, creating a wave that reached heights of 128 feet. This event not only reshaped the landscape but also posed a significant threat to nearby communities.

Key Takeaways

• Date of Event: December 4, 2007
• Location: Chehalis Lake, British Columbia
• Wave Height: 128 feet (38 meters)
• Speed of Wave: 59 mph (95 km/h)
• Damage: 10,000 trees, three campsites, and a boat launch destroyed
• No Casualties: No human lives lost due to the time of year

The Landslide That Started It All

On that fateful day, the tranquility of Chehalis Lake was shattered by a loud roar. A section of the mountainside east of Mount Ora collapsed, generating a landslide that moved at an astonishing speed of 134.2 km/h. This landslide was not just a minor event; it was a massive geological shift that would have dire consequences.

The Tsunami’s Impact

The landslide generated a tsunami that advanced across Chehalis Lake at a speed of 59 mph. Within just 30 seconds, the towering wave crashed against the eastern shoreline. Here’s a breakdown of the wave’s journey:

1. Initial Impact: 30 seconds to reach the eastern shoreline.
2. Northern Point: Another 15 seconds to hit the northernmost point of the lake.
3. River Surge: 15 seconds later, the wave traveled half a kilometer up the Chehalis River.
4. Continued Destruction: Over the next 3.25 minutes, the wave swept away thousands of coniferous trees lining the valley walls.
5. Final Surge: The wave reached the southern end of the lake, partially surging over the downstream portion of the Chehalis River.

Despite the extensive damage, including the destruction of three campsites and a boat launch, no lives were lost. The cold December weather had kept recreational activities at bay, which likely prevented potential casualties.

The Aftermath: Log Jam and Flood Risk

In the wake of the tsunami, thousands of floating logs formed a log jam, resembling a beaver dam. This created a new risk: a potential outburst flood that could threaten communities downstream. Fortunately, efforts to remove the debris blocking the river’s path were successful, alleviating the immediate danger.

Why Did This Happen?

The cause of the landslide and subsequent tsunami is complex. Typically, such events in Alaska or Canada are linked to retreating glaciers. However, in this case, no nearby glaciers had recently retreated. Instead, the region’s steep and rugged topography played a significant role.

• Historical Context: The area had been glacier-free for about 10,500 years.
• Pre-existing Conditions: Ground imagery revealed extensional cracks, indicating a slow landslide had been occurring unnoticed.
• Triggering Factors: The heaviest rainfall in 13 months lubricated the landslide block, leading to the catastrophic collapse.

Conclusion

The Chehalis Lake tsunami serves as a stark reminder of nature’s power. While the immediate impact was devastating, the lack of casualties highlights the importance of timing and environmental conditions. As we reflect on this event, it’s crucial to understand the geological factors that contribute to such disasters, ensuring we remain vigilant in monitoring and preparing for future occurrences.