Recent Western earthquakes and potential tsunamis

Several months ago, I featured an article about the recent earthquake activity in the western U.S. According to the U.S. Geological Survey, on Thursday, Dec. 5, a strong 7.0 magnitude quake was reported off the Northern California coast near Cape Mendocino and the town of Petrolia. Residents as far away as San Francisco felt the earthquake as thousands of people reported feeling a rolling motion when the quake hit that morning.

As is typical with large earthquakes, last Thursday’s event spawned numerous aftershocks. Based on data from the USGS, most were in the range of 2.5 to a high of 4.7 in magnitude. The earthquake also triggered a tsunami warning for over 5 million people in the coastal regions from southern Oregon southward to San Francisco. Fortunately, a tsunami didn’t materialize, and the warning was soon canceled.

People living in the western U.S., especially in California, are very familiar with earthquakes. However, tsunamis may be another matter. A tsunami is a large volume of water that will often resemble a rapidly rising tide along coastal areas, rather than appearing as a large breaking wave. Unlike normal ocean waves that are generated by winds, tides or the gravitational pull of the moon and the sun, a displacement in the ocean or large lake caused by earthquakes, volcanic eruptions, landslides and large meteorite impacts can generate one or more waves with heights up to 100 feet above sea level. One the largest waves ever observed occurred in 1958 in Alaska. A landslide in one of Alaska’s narrow bays resulted in a massive 1,700-foot wave.

The worst tsunami in recent times happened Dec. 26, 2004, as a 100-foot tsunami practically destroyed many communities that were along the coastlines of the Indian Ocean that killed near 228,000 people. The massive waves were generated by a major 9.2 to 9.3 magnitude earthquake that happened off the west coast of northern Sumatra, Indonesia.

On March 11, 2011, a 9.0 earthquake struck approximately 80 miles east of Sendai, Japan in the Pacific Ocean. Tsunami waves generated from the massive earthquake were estimated to be over 130 feet that hit Sendai and led to the Fukushima Daiichi nuclear disaster as three of the primary nuclear reactors melted down. There are many dramatic videos on YouTube that shows the massive tsunami waves inundating some of the coastal regions of Japan.

Back in 1700, on Jan. 26, an estimated 9.0 magnitude megathrust earthquake along the Pacific coast, a 700-mile stretch from British Columbia to California, led to a tsunami that hit the western coastlines of North America and the eastern coast of Japan. Tree rings and written records were used as evidence to determine the strength of the tsunami.

Tsunamis can also be generated in large lakes, mostly due to landslides. Most media reports will refer to them as “inland tsunamis,” but the destructive effects of those events are sometimes similar to the ones along coastal regions.

In Washington, there have been seven reported tsunamis at the Franklin D. Roosevelt Lake, which was created in 1941 by the impoundment of the Columbia River by the Grand Coulee Dam. Two of these events occurred in 2009 from landslides. On Jan. 16, 2009, a section of the shoreline at the mount of the Spokane River collapsed into the lake resulting in a wave height of 30 feet. On Aug. 25, 2009, there was a wave height of 20 feet that struck a local campground and carried some people into the lake. Fortunately, everyone survived the incident.

The massive eruption of Mount St. Helens on May 18, 1980, caused a major landslide into Spirit Lake in Washington. This led to a “megatsunami” that generated a wave of an incredible 850 feet high.

In terms of our local weather, after a period of cloudy and foggy days last week where the temperature only moved a few degrees from high to low, a storm system brought a wintry mix to the region Saturday.

Snowfall in the lower elevations has almost been non-existent so far this season. According to Cliff’s records of Coeur d’Alene weather dating back to 1895, the period from Nov. 1 through late Saturday has been the most snowless in recorded history. Most of the storm systems that have provided moisture have been too warm for snow in the valley locations.

A series of storms are expected to move through our region through the end of the month. Cliff and I expect to see some measurable snowfall toward the end of the week, but it may be a battle between the warmer air to the south and the colder air to the north on how much snow we receive. It’s always a temperature thing here in the Inland Northwest.

Our above-normal snowfall forecast was mostly based on the cooling of sea-surface temperatures along the equatorial regions that would ultimately lead to a new La Niña event.

However, the odds of a new La Niña forming are shrinking as ocean waters have warmed a bit along the West Coast of South America. It’s still early, but we’ll have a better idea of the chances for good winter snowfalls this season in the coming weeks.

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Contact Randy Mann at randy@longrangeweather.com.