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Tree rings give insights to past climates and earthquakes

by RANDY MANN
| December 11, 2023 1:05 AM

Tree ring data has become very important in determining a region’s past climate. Trees are sensitive to the area’s local climate and each year, the tree will grow rings, which also provides an age for the tree. Depending on the conditions during a particular year, a tree ring can give scientists a good idea of the local climate. For example, during warm and wet seasons, the tree rings are usually wider, but they are thinner when it’s usually cold and dry. If there are drought conditions, there may be limited growth.

By comparing tree ring data with local weather records since the late 1800s in many locations across the U.S., scientists can use that data to look at the region’s past climate beyond the period of weather observations. Many trees can live for hundreds and even thousands of years. One of the oldest living trees in the world, according to nasa.climate.gov, is the Methuselah Tree in White Mountain, Calif. It’s estimated that the bristlecone pine tree is almost 5,000 years old.

Based on the most recent estimations, there are over 3 billion trees on Earth, which is about eight times more than scientists thought about 10 years ago. However, 42 million trees are cut down each day.

In addition to providing past climate data, scientists have also determined that tree ring data can provide clues to major earthquakes. A recent study showed that some longer-living trees had a radiocarbon spike that signaled a massive earthquake in the Pacific Northwest. This data has helped to determine that the Seattle, Olympia, Tacoma and British Columbia region may have more faults that could eventually lead to a major earthquake.

The study concluded that several fault zones in the Northwest, based in part on tree ring data, did rupture around the year 923 to early 924 leading to an estimated 7.8 magnitude earthquake. The confirmation of these fault systems indicates that the northwestern coastal regions are susceptible to other earthquake faults that could also trigger a tsunami and create widespread major damage.

In addition to this fault system, the Pacific Northwest will eventually see another major earthquake along a different region called the Cascadia Subduction Zone. Major earthquakes in the Pacific Northwest are not very common, but scientists are concerned about a potential large event along the West Coast of Washington within the next 50 years.

Based on historical evidence, there was a huge megathrust earthquake Jan. 26, 1700, known as the 1700 Cascadia earthquake. It happened across a 620-mile area along the Cascadia subduction zone from the middle of Vancouver Island in British Columbia, Canada southward along the Pacific Northwest coast down into northern California. The magnitude was estimated between 8.7 and 9.2.

The big quake in 1700 was believed to have generated a large tsunami that hit the coast of Japan. It may also have been linked to the Bonneville Slide. This was a major landslide that dammed the Columbia River near Cascade Locks in Oregon. The Native Americans referred to this as the “Bridge of the Gods.” However, other investigations state that the landslide occurred around 1450 based on radiocarbon dating and tree ring data.

Geologic evidence shows that a major earthquake that would likely cause heavy damage to Seattle, Portland, Vancouver and other big cities along the Pacific Northwest coast, occurs approximately every 400 to 500 years. So, the chances of a major event within the next 30 are currently around 10%.

The most devastating earthquake in recent times was the Alaskan earthquake in 1964. It was the second largest recorded in history and measured a whopping 9.2. The largest earthquake that was measured happened in Chile in 1960 which had a magnitude of 9.5. This occurred along a subduction zone, where the Pacific Plate goes under the South American plate. The region is also referred to as part of the “Ring of Fire.”

In terms of our local weather, there has been plenty of moisture across the Inland Northwest, but much of it has fallen in the form of rain in the lower elevations. After a normal November for precipitation, the first 10 days of December have been wet with 3.29 inches of moisture at Cliff’s station in Coeur d’Alene. However, only 7.9 inches of snow has fallen as the air masses have been too warm.

As we’ve mentioned numerous times, there is a strong El Niño sea-surface temperature pattern and our region often has much less snow during these events. However, in the higher mountains, there are reports of at least 2 feet of snow on the ground.

Looking farther ahead, the long-range computer models are showing more showers moving across our region through the end of the month. Prior to the Christmas holiday, there is a chance of rain or snow in the Coeur d’Alene region with snow in the higher mountains. Depending on temperature, there is still a chance for a White Christmas, but it’s a small chance.

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Contact Randy Mann at randy@longrangeweather.com.