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Waning Pleistocene Ice Sheet Affected Megaflood Paths and Local Shorelines

February 20, 2022

Have you ever thought about the how the weight of the ice-age Cordilleran ice sheet might affect the underlying Earth’s crust. There is strong evidence that the crust was depressed hundreds of feet beneath the ice, and since the crust is relatively thin and rigid over a plastic aesthenosphere, that also caused the crust for some distance beyond the ice margins to tilt toward the ice sheet. A new modeling study explored how changes in topography due to the solid Earth’s response to ice sheet loading and unloading might have influenced successive megaflood routes over the Channeled Scablands between 18 and 15.5 thousand years ago. The modeling found that deformation of Earth’s crust may played an important role in directing the erosion of the Channeled Scabland. Results showed that near 18 thousand year old floods could have traversed and eroded parts of two major Channeled Scabland tracts—Telford-Crab Creek and Cheney-Palouse. However, as the ice-age waned and the ice sheet diminished 15.5 thousand years ago, crustal isostatic rebound may have limited megaflood flow into the Cheney–Palouse tract. This tilt dependent difference in flow between tracts was governed by tilting of the landscape, which also affected the filling and overspill of glacial Lake Columbia directly upstream of the tracts. These results highlight one impact of crustal isostatic adjustment on megaflood routes and landscape evolution. Other studies have shown that relative ice-age sea levels were over 300 feet lower worldwide due to the volume of water locked up in ice sheets. Typical depictions of the shoreface extent are generally based on a 300 ft. depth contour, but there is strong evidence that shorelines were up to 200+ ft. higher than present day in marine areas adjacent to ice sheets, again because the crust was depressed by the weight of the ice sheer. A more accurate representation might show a much narrower shoreface in ice-free areas nearer to the ice sheet margin. However, in the Haida Gwaii Strait at the margin of the ice sheet the lower thickness of the ice sheet meant that local shorelines were as much as 550 feet lower than they are today. This was because the much greater thickness of the center of the ice sheet served to push upwards areas at the edge of the continental shelf in a crustal forebulge. It is now widely thought that these emergent ice-free land areas might have provided a viable coastal migration corridor for early peoples making their way to the Americas from Asia during the Pleistocene.

The Columbia River Gorge Eagle Creek Fire – Ruin or Renewal?

October 11, 2017

I’ve found there is huge public interest and concern about the catastrophic effects of the Eagle Creek Fire on the Columbia River Gorge. Pictures of ridgeline after ridgeline enveloped in bright orange fire, trees bursting into towering flames, and the choking smoke that filled valleys throughout the Pacific Northwest are truly a hellish image of Armageddon visited on the entire area. But, while the temporary loss of recreational trails and green forest aesthetics, and the increased potential for landslides and falling snags are inconvenient and even somewhat dangerous, the truth is that the recent fires have not ruined the natural areas of the West and the Gorge in particular, but instead have refreshed and renewed them. This past summer I’ve been interpreting geology for a new Columbia Gorge Master Naturalist Program, working beside forest ecology experts who are extremely optimistic regarding the effects of the Eagle Creek Fire. One of those experts, wildlife habitat expert Bill Weiler, writes, “Life will return to burned areas in short order. Fungi are already crawling around in the ashes of the fire, laying the foundation for soil that will support the plants that will constitute the early stage of the forest’s re-growth—a time when heat from the fire and sunlight newly reaching the ground in the absence of a canopy encourages a new crop of plants to firm up the soil structure that will allow gigantic trees to thrive. And ash is nature’s fertilizer. Plant blight, disease and insects are reduced or eliminated by burns. Mineral soil is the compost that Douglas fir seedling roots need to grow. “Dead trees” or snags are full of life.” In a typical forest fire a third of the trees will be scorched and dead, a third will be moderately to severely damaged, and a third will be essentially unscathed. Reports from the Eagle Creek Fire describe that fire as a discontinuous “mosaic burn” with much less devastation even than the typical forest fire burn. There is a broad consensus among scientists that we have considerably less fire of all intensities in our Western U.S. forests compared with natural, historical levels, when lightning-caused fires burned without humans trying to put them out. Early in the 20th century, before fire suppression became the norm, the average annual burn area in the western states was over 25 million acres, compared to a recent average of 4-6 million acres. According to Oregon State University Professor John Bailey, a century’s worth of suppressing wildfire in the United States has created conditions, especially in the West, that will ensure longer fire seasons because of longer, drier and hotter summers. Those conditions point to the need for “actively managed” forests which could include more deliberately set and managed prescribed fires. “Easily two-thirds or more of the Gorge fire is really good ecological fire,” Professor Bailey said, “the fire does some of the fuel management for us.” There is an equally strong consensus among scientists that fire is essential to maintain ecologically healthy forests and native biodiversity. This includes large fires and patches of intense fire, which create an abundance of biologically essential standing snags and naturally stimulate regeneration of vigorous new stands of forest. These areas of “snag forest habitat” are ecological treasures, not catastrophes, and many native wildlife species depend on this habitat to survive. More than 260 scientists wrote to Congress in 2015 noting that snag forests are “quite simply some of the best wildlife habitat in forests. ” Much of the Eagle Creek Fire burn area is closed to civilian activities due to the danger from flare-ups, rock slides and falling snags. The fire is less than 50% contained due to the ruggedness and inaccessibility of much of the area. Though it is still burning it is not expected to flare-up again until Winter rains and snow completely douse the embers.

The Cerutti Mastodon Site – A Bretz Type Controversy of Our Time

May 3, 2018

In March, while visiting San Diego, I went to the San Diego Museum of Natural History in Balboa Park and toured the remarkable Cerutti Mastodon Site exhibit. This controversial exhibit of a mastodon site is notable for its claim that the mastodon’s bones were broken by humans 130,000 years ago, making it far older than any other such site in North America. The signs at the beginning of the exhibit read as follows; “The Cerutti Mastodon discovery. A San Diego find reveals the earliest evidence of of human life in North America. In 1992, paleontologists from the San Diego Natural History Museum were surveying a highway construction site to identify and salvage any fossils that might be unearthed. “Field paleontologist Richard Cerutti spotted some bones and tusks. Exploring further, the team discovered that these were bones of a mastodon-an extinct relative of elephants. “But Richard noticed something unusual. The bones were mysteriously broken and the pieces separated. “It took 22 years for scientists to solve the riddle. Once they did, they realized that this local site is evidence of human presence on this continent 130,000 years ago-much earlier than we thought possible. “In 2014, scientists made a new discovery about the age of the Cerutti Mastodon Site. How did this happen? Scientists figured out the age of the mastodon bones using radiometric dating. It’s a way of telling how old a rock or fossil is by measuring its radioactive isotopes. “A radioactive isotope transforms into an isotope of a different element over time. If you know the rate at which the “parent” isotope transforms into its “daughter” isotope, measuring the parent-daughter ratio tells you how old the material is. “Scientists used a method that measures the ratio of the radioactive isotope uranium-234 to its daughter isotope thorium-230. Dramatic improvements in this method have made it a highly accurate means of dating very old materials- up to 500,000 years. In 2014, scientists used this method to date bones at the Cerutti Mastodon Site. “The results were clear. The bones are approximately 130,000 years old.” More than two decades after the Cerutti mastodon’s discovery in southern California in 1993, USGS scientist Dr. James Paces was sent several bones of unknown age. The specimens were important because they came from a site with abundant evidence of processing by ancient humans. Advances in analytical capabilities and the understanding of processes that incorporate natural uranium and its decay products in fossil bone provided archaeologists with a radiometric dating tool that, at least in some cases, could confidently and accurately determine ages for these older materials. After analyzing nearly 100 subsamples from multiple specimens, Dr. Paces determined that the mastodon bones—which were still fresh when someone fractured them using hammerstones and rock anvils—were covered with sediments 131,000 years ago, give or take about 9,000 years. This result indicates that some form of archaic humans arrived in the Americas more than 100,000 years earlier than scientists had thought possible. Following the dating of the bones officials at the Natural History Museum began making plans for a permanent exhibit about the discovery. The exhibit opened in 2017. It is very thorough and includes bones, alleged hammerstones, and anvil rocks from the original mastodon site as well as numerous photos and interpretive panels. When J Harlen Bretz first announced in the 1920’s his theory that the scablands of eastern Washington State had been carved out by a cataclysmic flood he met stiff opposition. What he was proposing was so far out of the mainstream of geological thinking of the time that many scientists couldn’t accept it. Schooled in uniformitarianism they believed that earth’s landforms were all created by slow gradual processes operating over time and that an event of the magnitude Bretz was proposing just wasn’t possible. They tried to come up with alternative explanations for the facts Bretz presented that fit in with their current frame of reference. Yale University geologist Richard Foster Flint famously said of certain flood features in the scablands that they presented “a picture of leisurely streams with normal discharge.” The claim by San Diego’s Natural History Museum that the Cerutti site is 130,000 years old is likewise far outside what many scientists of our time are ready to accept. Other similar sites are much younger. For example Sequim’s famous mastodon site is only 13,800 years old. If the San Diego Natural History Museum is correct it totally rewrites the history books about humans in North America. It places humans in North America during a previous interglacial period. It would establish that humans had long since been in North America during the time of the comparatively recent ice-age floods. Critics of the Natural History Museum, and there are many, point to things like what they consider to be a lack of lithics from the site. Others speculate that the signs of bone breakage observed at the site may have been caused by some other creature besides humans or by modern day construction equipment. But the Natural History Museum counters that none of the critics have provided a satisfactory alternative explanation for the evidence that they’ve presented. Cerutti and his team of researchers and the San Diego Natural History Museum remain unequivocal in their conclusion: The Cerutti Mastodon Site is a 130,000 year old archaeological site. – by Mark Sundquist, Puget Lobe Chapter “Ideas without precedent are generally looked upon with disfavor and men are shocked if their conceptions of an orderly world are challenged.” J Harlen Bretz 1928 “Extraordinary claims require extraordinary evidence – each aspect requires the strongest scrutiny,” Chris Stringer

Pillow Basalt and Palagonite – Lava Flowing into Water

November 4, 2015

Pillow basalt and palagonite are the result of lava flowing into water. We have a striking example in the Columbia River Gorge at the intersection of Hwy 30 and US 197 at the east end of The Dalles. This video gives a good idea of how these basalt pillows form and what they look like.

Hiking Drumheller Channels

July 14, 2022

Hiking Drumheller Channels Ice Age Floods National Geologic Trail There are scads of hiking trails all through Drumheller Channels National Natural Landmark. On a cloudy day in early June we took off on a couple of exploratory hikes that were simply amazing. We first proceeded south from the parking lot at Lower Goose Lake, running through late Spring wildflowers, eventually looking for one of Bruce Bjornstad’s geocaches. We wandered over hills and down into deeper valleys, always surrounded by the towering walls of basalt defining that section of Drumheller Channels. Along the way we found an area of apparent Kolk depressions with odd spires of basalt poking up out of the middle of a central mound. Soon we passed through a reedy area that bounded the southern edge of Lower Goose Lake. We continued on south to the edge of Black Lake where the geocache was supposed to be, but after 20 minutes with 4 of us looking in the area of the GPS coordinates, we finally decided the cache was no longer there and headed back. The hike was easy, very pleasant, and mercifully cool due to the cloudy morning. We then drove north across the O’Sullivan Dam, and back south through Columbia National Wildlife Refuge to the W. McManamon Road entrance to Crab Creek Marsh Unit #3 and the Basalt Columns at Drumheller Trailhead, the kickoff point to go to the top of “Nick’s Columns”. Nick Zentner’s videos about the columns are great, but the blooper where his rock hammer falls down between columns is priceless. We just had to see those columns for ourselves, and we weren’t disappointed. It’s interesting how only the columns along the edge are free standing, while those inboard are packed around with sediment. The little rain the area gets probably washed the sediment out of the spaces between the bordering columns. After walking around for a while we made our way back to the car and drove to the Drumheller Channels National Natural Landmark overlook for a final sweeping viewpoint. The entire area is huge and worth several days of exploring, but it’s also pretty easy to have a great time in just a few hours. This is a place you just have to experience. Quick Facts Location: Adams County, Washington 99371

Castle Lake Basin

July 16, 2017

Castle Lake fills a plunge-pool at the base of a 300-ft tall cataract at the opposite (east) end of the Great Cataract Group from Dry Falls, above the east end of Deep Lake. A set of steel ladders put in place during the construction of the Columbia Basin Irrigation Project allow for a safe descent into the basin. In the basin are great views of giant potholes, the flood-sheared face of Castle Rock, as well idyllic Deep Lake. The Castle Lake Basin lies along the east end of the Great Cataract Group. At the base of the cataract is lovely blue-green Castle Lake plunge pool nestled into the rock bench below. Castle Lake lies within a single recessional cataract canyon eroded down to a flood-swept, pothole-studded rock bench that stands 100 feet above Deep Lake. This is the same rock bench of Grande Ronde Basalt where dozens of potholes occur at the opposite (western) end of Deep Lake. Castle Rock itself is an isolated butte along the west side of the Castle Lake basin. It is a faceted butte escarpment nearly sheared off by monstrous flood forces moving across the cataract.

Bering Land Bridge Formed Surprisingly Late During Last Ice Age

December 27, 2022

By reconstructing the sea level history of the Bering Strait, scientists found that the strait remained flooded and the Bering Land Bridge connecting Asia to North America did not emerge until around 35,700 years ago, less than 10,000 years before the height of the last ice age (known as the Last Glacial Maximum), and not long before humans are thought to have begun migrating into the Americas. The new findings indicate that the growth of the ice sheets—and the resulting drop in sea level—occurred surprisingly quickly and much later in the glacial cycle than previous studies had suggested. “It means that more than 50 percent of the global ice volume at the Last Glacial Maximum grew after 46,000 years ago,” said Tamara Pico, assistant professor of Earth and planetary sciences at UC Santa Cruz and a corresponding author of the paper. “This is important for understanding the feedbacks between climate and ice sheets, because it implies that there was a substantial delay in the development of ice sheets after global temperatures dropped.” Global sea levels drop during ice ages as more and more of Earth’s water gets locked up in massive ice sheets, but the timing of these processes has been hard to pin down. During the Last Glacial Maximum, which lasted from about 26,500 to 19,000 years ago, ice sheets covered large areas of North America. Dramatically lower sea levels uncovered a vast land area known as Beringia that extended from Siberia to Alaska and supported herds of horses, mammoths, and other Pleistocene fauna. As the ice sheets melted, the Bering Strait became flooded again around 13,000 to 11,000 years ago. The new findings are interesting in relation to human migration because they shorten the time between the opening of the land bridge and the arrival of humans in the Americas. The timing of human migration into North America remains unresolved, but some studies suggest people may have lived in Beringia throughout the height of the ice age. “People may have started going across as soon as the land bridge formed,” Pico said. The new study used an analysis of nitrogen isotopes in seafloor sediments to determine when the Bering Strait was flooded during the past 46,000 years, allowing Pacific Ocean water to flow into the Arctic Ocean. First author Jesse Farmer at Princeton University led the isotope analysis, measuring nitrogen isotope ratios in the remains of marine plankton preserved in sediment cores collected from the seafloor at three locations in the western Arctic Ocean. Because of differences in the nitrogen composition of Pacific and Arctic waters, Farmer was able to identify a nitrogen isotope signature indicating when Pacific water flowed into the Arctic. Pico, whose expertise is in sea level modeling, then compared Farmer’s results with sea level models based on different scenarios for the growth of the ice sheets. “The exciting thing to me is that this provides a completely independent constraint on global sea level during this time period,” Pico said. “Some of the ice sheet histories that have been proposed differ by quite a lot, and we were able to look at what the predicted sea level would be at the Bering Strait and see which ones are consistent with the nitrogen data.” The results support recent studies indicating that global sea levels were much higher prior to the Last Glacial Maximum than previous estimates had suggested, she said. Average global sea level during the Last Glacial Maximum was about 130 meters (425 feet) lower than today. The actual sea level at a particular site such as the Bering Strait, however, depends on factors such as the deformation of the Earth’s crust by the weight of the ice sheets. “It’s like punching down on bread dough—the crust sinks under the ice and rises up around the edges,” Pico said. “Also, the ice sheets are so massive they have gravitational effects on the water. I model those processes to see how sea level would vary around the world and, in this case, to look at the Bering Strait.” The findings imply a complicated relationship between climate and global ice volume and suggest new avenues for investigating the mechanisms underlying glacial cycles. In addition to Pico and Farmer, the coauthors include Ona Underwood and Daniel Sigman at Princeton University; Rebecca Cleveland-Stout at the University of Washington; Julie Granger at the University of Connecticut; Thomas Cronin at the U.S. Geological Survey; and François Fripiat, Alfredo Martinez-Garcia, and Gerald Haug at the Max Planck Institute for Chemistry in Germany. This work was supported by the National Science Foundation. Published in Proceedings of the National Academy of Sciences. Reprinted from UC Santa Cruz Newsletter, By Tim Stephens

Relive Important Archive Articles

The Cerutti Mastodon Site – A Bretz Type Controversy of Our Time

Pillow Basalt and Palagonite – Lava Flowing into Water

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