Blue Mountains from Baker City, Oregon. Photo by D. Kerr, Wikimedia Commons
Continuing on our drive to Seattle we crossed over the Blue Mountains in eastern Oregon. To the overland traveling covered wagons on the Oregon Trail , the Blue Mountains were the last big barrier to overcome before reaching the rich farmlands of Oregon and Washington. In contrast to the struggle the waggoneers had to endure to get over this last range, we raced up and over the mountains effortlessly on the four-lane Interstate. The slopes of the mountains were covered with pine trees many of which show significant mountain pine beetle (MPB) damage (see Signs of Spring 11, May 13, 2021). Just past the mountains we came to Baker City Oregon (elevation 3451’) which sits on the edge of the Columbia Plateau (also called the Columbia Basalt Plain). We are about to enter a landscape that is very different from anything we have seen so far on this trip!
The Columbia Plateau is a wide lava plain that formed six to sixteen million years ago as the result of a series of massive volcanic eruptions. Geologists have identified three hundred, different, high volume point sources of lava across the plain and assume that there were actually many more lava release points that have been obscured by later occurring eruptions. They also speculate that most of the lava (which covers 100,000 to 200,000 square miles in the states of Washington, Oregon and Idaho (for some reason the area estimates of plain vary widely in different references!)) was released during the first million and half years of the eruption event. The lava is six thousand to ten thousand feet thick and so massive that its weight has crushed the crustal rocks beneath it and caused an extensive surface subsidence. The surface of this extensive plateau, then, is at a very modest elevation (only 400’ to 4000’ above sea level).
Map of the Columbia Plateau, L. Topinka, USGS. Wikimedia Commons
The plain is bordered on the west by the Cascades, on the east by the Rockies, and on the south by Basin and Range. When the lava flowed, it filled the river canyons and then overtopped all but the tallest mountains across the ancient landscape and generated a new surface topography of flat plains and mounded, rolling hills. The Columbia River and many of its tributaries have cut new canyons through the basalt. Many of these canyons are quite deep and reveal the layers and layers of lava rocks and flows.
The oldest lava in the plain is found on its western edges and the youngest on its eastern edge near Yellowstone Park. One inference from this rock-age sequence is that the causative agent for this lava release was slowly moving across the landscape, or, more precisely, that the landscape (which sits on the westward moving North American tectonic plate) was slowly moving across a heat source of unbelievable energy and intensity. Current hypothesis about this event link it to the Yellowstone Hot Spot that a few million years later created the Snake River Plain to the south (see Signs of Summer 4, June 24, 2021) and that today sits under Yellowstone National Park.
Columbia River near Kenniwick. Photo by K. Lund, Flickr
We cross the Columbia River near Kennewick, Washington. The river looks so slow and controlled! The flow control and hydroelectric power dams that have been constructed on the Columbia have reduced it to a very tame waterway! We are surrounded by red-bare hills that look more Martian than Terran! Annual rainfall here is less than ten inches, but the abundance of irrigation water from the nearby Columbia and its tributaries enables extensive agricultural activity. We see large fields of fruit trees covered by protective netting to keep the birds from consuming the fruit. We see acre after acre of grapes and signs for local wineries. Hay fields, alfalfa fields, sugar beets and potatoes are grow in these irrigated fields. There are also wheat fields off to the west.
Vineyards on Columbia Plateau. Photo by D. Sillman
We went to a wine tasting at a winery north of Seattle a few days later and heard about the dry, powdery soils and the annual rainfall of no more than five inches that defined the vineyards out here in Eastern Washington (specifically a vineyard near Redmund, Washington where the Seattle winery grows its grapes) . The story of the founding of these vineyards in the early part of the 20th Century and leap of faith that the grape farmers had to make to try to grow grapes in this foreboding environment was inspirational. The sommelier at the winery also talked about the impact of water stress on wine grapes. Giving the vines slightly less water than they “would like” (highly controlled irrigation regimes) makes the grapes smaller, thicker skinned and more densely packed with tannins and other flavonoids. This helps to create the distinctive flavor profiles of the finished wines. We tried four wines from this “desert” region, and they were each distinctive and delicious!
Hops field. Photo by I. Sane, Flickr
Another crop that was planted and just starting to grow in these dry fields is hops. Most of the hops grown in the United States is grown here on the Columbia Plateau. We could see the tiny, initial green growth of the hops plants underneath their tall, distinctive poles and systems of support wires. By late summer the hops vines will have wound themselves up around the wires and be covered with their sharp tasting flower clusters and strobiles.
Yakima River and surrounding hills. Public Domain.
We drive on toward the Cascades! Near Yakima, Washington we pass a series of absolutely bare, brown, rounded sandy hills and mountains. The pillowed up underlying lava has created a strange, gigantic, mogul-like topography! The soils are incredibly dry due to the rain shadow of the Cascade Range. The line of the mountains delineates the two, ecological extremes that define Washington State: the wet, temperate coastal biomes to the west of the range and the semiarid and arid grasslands to the east.
We cross the Cascade Range through Snoqualmie Pass (elevation 3022’). The drive up the western slope of the pass is tucked in to the surrounding mountains which are densely covered with lodgepole pines, ponderosa pines, grand fir and Douglas-fir. I had hoped to catch a glimpse of some of the famous volcanic peaks off to the south and to the north of the pass, but the topography and tall trees prevented it.
Cascade volcanic arc. Figure by NASA,. Public Domain
The Cascade Range overlies a long, subterranean line where the off-shore, Juan de Fuca tectonic plate (which is 90,000 square miles in area!) is sliding under the even more massive North American tectonic plate (which runs from the Pacific to the Atlantic Ocean!). This zone of interaction between these two plates generates the Cascadian Subduction Zone which has created the Cascade Range and fuels the volcanoes that are lined up in it.
To the south of Snoqualmie is Mt. Rainier (which is easily visible from Seattle on a clear day), Mt. Adams and the most recently erupting of these Cascade volcanoes, Mt St. Helens. The chain of southern volcanoes goes well down into Oregon (Mt. Hood) and California (Mt. Shasta). To the north of Snoqualmie is Mt. Baker (which we saw filling up the eastern horizon when we were out on the Olympic Peninsula a few years ago), Glacier Peak and then a line of peaks that stretch on up into Canada. These are all active or potentially active volcanoes and are visible evidence of the underlying stresses of the interacting tectonic plates.
Mt. St. Helens after eruption. Photo by L. Topinka, Wikimedia Commons
Mt. St. Helens erupted on May 18, 1980. The eruption was preceded by a series of earthquakes and seismic activity. The force of the eruption collapsed the north face of the mountain sending almost four million cubic yards of mud and debris toward the Columbia River. The pyroclastic flow generated by the explosive eruption flattened trees and buildings over a 230 square mile area and released one and a half million tons of sulfur dioxide into the atmosphere. The peak of the mountain was literally blown away and the resulting apex of the volcano was 1300’ lower than its pre-eruption configuration.
The ash cloud rose up sixteen miles into the atmosphere and was pushed east by the upper level winds at sixty miles per hour. On May 20, 1980, I happened to be driving across Missouri on my way to Tulsa, Oklahoma, and I saw the streaking cloud of volcanic dust stretched out to the north.
Mt. St Helens exploded with 24 megatons of thermal energy, ejected 0.67 cubic miles of crustal materials into the atmosphere, killed 54 people and 7000 large animals (deer, elk and bears), and was the most violent volcanic explosion in recent North American history. But, many other historical and recent volcanic eruptions have been much larger and much more powerful!
Crossing the pass, the road begins to descend to the near sea level altitudes in and around Seattle. The trees lining the Interstate change from the species that thrived in the drier conditions of the west to species that are more adapted to the wetter conditions of the ocean-facing slopes: Douglas-fir persists but now intermixed with western hemlock, western red cedar and Pacific silver fir.
We enter the late rush hour traffic of Seattle and follow the signs and directional prompts from our phone to get to Joe and Marlee’s house in Lake City on the northeast side of the city. Elevation 243’ above sea level, lots of oxygen to breathe, and a great place to park our car for a while!