Site hosted by Angelfire.com: Build your free website today!

Setting the Stage for the Ice Age Floods


Text by Nick Zentner
Department of Geological Sciences
Central Washington University

Sweat pours off your brow on a humid morning 16 million years ago in central Washington. The sun is rising high in the southern sky as you hike on a favorite trail to one of the many lakes of central Washington. The trail winds through a forests of alder, oak, maple, cypress, and the magical ginkgo. The landscape rolls on before you – gently rolling hills that steam in this world that averages 75 degrees F and relative humidity of 75 percent.

One morning, a distant rumble on the eastern horizon causes concern. A wildfire? Sure, but this is no ordinary fire. The trees are burning as a jaw-dropping flood of orange lava marches into your beloved hiking paradise. The lava is unrelenting as it ignites trees and blankets the lake. Steam pours over the landscape as the lava continues to bulldoze its way to the Pacific Ocean – perhaps encroaching over this humid land at the pace of a brisk walk. You have decided to move at a rate decidedly faster than a brisk walk!

Science fiction? Yes and no. Humans were not on planet Earth 16 million years ago. The fossil record tells us that life flourished in the Northwest at that time, but human-like creatures did not make an appearance until roughly 4 million years ago - and that was in Africa. However, the landscape of your morning hike has been carefully recreated from painstaking research completed by hundreds of field geologists that have worked in our region over the last century. Lost worlds are hidden in the basalt bedrock beneath cities like Spokane, Pasco, and Portland.



Flood Basalts on Planet Earth

The Columbia River Basalts of the Pacific Northwest (16 Million years ago) are well known to geologists around the world, but there are similar piles of flood basalt in central India (66 Ma), southern Brazil (132 Ma), southern Africa (183 Ma), and central Siberia (248 Ma).. In each case, very large volumes of basaltic magma erupted rapidly from cracks in the continent to form sheets of lava rock covering tens of thousands of square miles.

Many scientists believe that these spectacular eruptions – more than 300 distinct events punctuated by 10,000 years of quiet between each lava flood - must have had a profound effect on the world climate. Large volumes of sulfur dioxide accompany these kinds of eruptions. 1.7 megatons of SO2 was erupted per day during the relatively tiny 1783 eruption in Iceland. In comparison, a single flow of the Columbia River flood basalt province is estimated to have produced more than 12,000 megatons of SO2 over a ten year period. And this was just one of the hundreds of flows!
Volcanoes around the world come in different shapes and eruptive styles. Low and broad volcanoes that erupt fluid rivers of lava are usually found in the oceans. Beautiful cone-shaped volcanoes that erupt with violent ash clouds are usually found near the coasts of continents. Terrifying caldera-forming volcanoes that have the potential to kill thousands are found inland on continents.





The Columbia River Basalts of the Pacific Northwest are an exception to the global rule! Oceanic lavas have flooded the continent from below much like a boat with a leak. The cracks in the bottom of the boat in this case are called fissures. Fissures Deliver Staggering Lava Floods Fissures - tens of miles long - cracked the North American crust in southeastern Washington and northeastern Oregon 17 million years ago. Spectacular floods of runny magma issued forth from the cracks and began transforming the rugged inland landscape of the Northwest. The opening act – dozens of small lava flows traveled only tens of miles from their source as they filled steep canyons and valleys flow by flow.


The headliners of the CRB show were the mighty Grande Ronde flows which covered hundreds of miles due their impressive volumes and the previous grunt work of the canyon-filling Imnaha flows. Dozens of Grande Ronde flows reached the Pacific Ocean! Much of the rugged Oregon coast is composed of basalt lava rock that erupted near Idaho! In eastern Washington, Steptoe Butte and neighboring mountain peaks were tall enough to withstand the volcanic onslaught and kept their chins above the lava floods. Kittias County landmarks such as Table Mountain and Lookout Mountain mark the margin of the basalt floods as they crept across Kittitas County. Fissure Origins? During much of the 20th century, the origin of the fissures and the source of the Columbia River Basalts seemed a mystery, though there were many good ideas. Did the fissures develop as an oceanic spreading center was overridden by North America? Were the fissures related to the active stretching of the Basin and Range Province further to the south? Was the basaltic magma somehow related to the subduction off of the Northwest coast? Do the fissures mark the site of a dramatic meteorite impact? There were problems with each of the hypotheses. Presently, most geologists agree that the basalts and the fissures of the Columbia River Basalts are directly related to the heat that powers Old Faithful in Yellowstone National Park. In Wyoming! How in the world can the rock layers of Manastash Ridge be related to our oldest National Park? Here’s the story: Worldwide, hot spots power famous volcanoes – Hawaii, Iceland, Yellowstone - in a variety of settings. A hot spot is a stationary, deep-seated source of melted rock that continues its magma production even if a continent sits above! North America is slowly - but steadily - moving 2 inches per year to the southeast. The stationary hot spot is lurking below Yellowstone today, but where was the hot spot 16 million years ago? It was centered beneath eastern Oregon! Familiar Features in Central Washington How is it possible for a single lava flow to travel more than 300 miles? Debate rages among geologists, but many believe that lava transportation just below the surface, rather than surface flow, may account for the huge areas covered by basalt flows. Individual sheet flows show virtually no change in chemical composition and a very small drop in temperature from the start of the journey (fissures in southeastern Washington) to the end of the line (the coast). Did the flows steamroll over the landscape or are many of these flows essentially a bunch of lava tubes, with much of the lava transport happening just below the surface? The discussion continues… Lovers of our basalt-rich landscape are well aware of features like columns and vesicles, and to a lesser extent – pillow structures, palagonite, and entablature.


Basalt columns are perhaps the best known feature on the Columbia Plateau. The columns are simply cooling cracks that developed as the lava flow solidified. Many of the larger flows must have ponded as vast lava lakes taking up to years to solidify. Temperatures of the orange magma approached 1200 degrees Centrigrade. during the eruption, but as the flow began to cool, the top and bottom surfaces hardened first while the interior was still hot. Polygonal cracks form as the ‘skin’ cools and contracts (much like the cracks in a drying mud puddle after a storm). Finally, as the flow interior begins to cool, the surface cracks begin to propagate inward (like a giant stop sign-shaped cookie cutter being pressed into the flow). Evenly spaced, horizontal cracks within some columns indicates that the inward cooling of some flows perhaps up to a decade!


Columnar cracks can exhibit a two- or three-tiered arrangement much like a beautiful wedding cake. The bottom tier - the colonnade - consists of thick, usually well formed vertical columns. The second tier - the entablature - is usually a layer of thinner, less regular, often chaotic columns that are highly irregular in structure. There may be an upper colonnade forming a third tier. The columns can can develop from the top down or the bottom up, but keep in mind that if geologists are still debating the mode of lava transportation, then addressing colonnade and entablature geometries is tricky business! Have you ever been curious when you find a chunk of basalt shot full of pea-sized holes? The holes - called vesicles - form as bubbles of gas race to the top of a cooling lava flow. The vesicles are the bubbles that don’t complete their escape. Geologists create elaborate maps of the various basalt layers use vesicular zones as markers for the tops of the flows.

Divers off of the coast of the Big Island of Hawaii have photographed the basaltic lava flows underwater as the flow continue. Does the lava behave differently as it moces underwater? The answer is yes. Instead of moving as a sheet over land, the flow splits into fingers of movement underwater. Steam pours off of the water’s surface, but underwater these noodles of lava continue through the water. Many CRB flows have a curious collection of black, circular features at their base with crumbly, orange material surrounding it. The black circles (pillow structures) are interpreted to be fingers of lava pushing into water. Evidence for ancient lakes in central Washington! The orange material (palagonite) is interpreted to be devitrified obsidian – shiny, chilled volcanic glass that has broken down and rusted through time.

Using vesicular flow tops and pillow-rich bases as a guide, basalt enthusiasts can then carefully locate exciting time capsules between eruptions. That is, the boundaries between flows can reveal lost worlds that thrived for centuries between eruptions. In the warm and relatively moist climate of this time, there was sufficient time for soils to develop, forests to grow, and complex ecosystems to establish themselves. Many times, the border between flows is a simple amount soil layer (paleosols). In other cases, the border is marked by a sediment layer ( a clay layer, or sandstone, or diatomaceous earth). Careful study of the sediment can lead to the resurrection of an ancient lake, ancient stream system, or in come cases, and ancient forest. That’s right, the famous petrified wood of central Washington is a remnant of ancient forests that thrived in the time windows between devastating lava floods. Each layer of petrified wood represents a different forest ecosystem that dominated our region. Why didn’t the trees burn as the lava covered the scene? Most did, but some logs were underwater in the lake and the water protected the wood from the inferno that raged above. Therefore, not all petrified wood comes from the same layer. The Vantage Sandstone (first studied near Vantage, WA) has yielded the most impressive logs (including the much-desired ginkgo wood), but there are others of wood layers that cross the region. Yakima Fold Belt But, following these layers from county to county isn’t as easy as you’d think because the basalt layers (and the wood layers between them) have been folded and faulted numerous times. For example, the Vantage SS is found at a number of elevations through the Yakima River Canyon between Ellensburg and Yakima. Why is this? Careful mapping of the canyon has made it clear that the region has been folded in a series of anticlines and synclines – with some reverse and thrust faults thrown in for good measure. The result? The Yakima Fold Belt of central Washington. Why the deformation? The fold and faults all tell the story of crustal squeezing over the last 7 million years. Compression from the south. Currently, our view is that northern California is creeping northward to deform the Pacific Northwest. Manastash Ridge, Saddle Montains. Seattle Fault, all owe their existence to the squeeze from the south. Encyclopedia of Volcanoes 2000 Academic Press Volcanic Successions: Modern and Ancient R. Cas & J. Wright, 1987 Allen & Unwin, Inc. In Search of Ancient Oregon Ellen Morris Bishop, 2003 Timber Press

Page 14