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Pacific Northwest

Glacier loss and the consequences for streamflow and sea levels

On an afternoon when I was working through some edits on a manuscript detailing the role of glacier melt water in sustaining agricultural water supplies in the Hood River valley of Oregon, it was more than appropriate that my good friend Chris Rowan should send me the link this beautiful and scary TED talk on photographic evidence of rapid ice loss from glaciers around the world..

How much are those retreating glaciers going to add to global sea levels under projected warming scenarios? By one recent estimate, up to 2 m by the end of the century, though more realistically 0.8 m in that time frame. Not such good news for those like to vacation on the Outer Banks or enjoy the majestic beauty of glaciers capping Oregon’s volcanoes.

GSA Abstract: On a template set by basalt flows, hydrology and erosional topography coevolve in the Oregon Cascade Range

The Watershed Hydrogeology Lab is going to be busy at this year’s Geological Society of America annual meeting in Portland, Oregon in October. We’ve submitted four abstracts for the meeting, I am co-convening a session, and I’ll be helping lead a pre-meeting field trip.

I’ll be an invited speaker in a session on “Hydrologic Characterization and Simulation of Neogene Volcanic Terranes (T27)” and here’s my abstract:

On a template set by basalt flows, hydrology and erosional topography coevolve in the Oregon Cascade Range

Anne Jefferson

Young basalt terrains offer an exceptional opportunity to understand landscape and hydrologic evolution over time, since the age of landscape construction can be determined by dating lava flows. I use a chronosequence of watersheds in the Oregon Cascade Range to examine how topography and hydrology change over time in basalt landscapes. Western slopes of the Oregon Cascade Range are formed from lava flows ranging from Holocene to Eocene in age, with watersheds of all ages have similar climate, vegetation and relief. Abundant precipitation (2.0 to 3.5 m/yr) falls on this landscape, and young basalts are highly permeable, so Holocene and late Pleistocene lavas host large groundwater systems. Groundwater flowpaths dictated by lava geometry transmit most recharge to large springs. Spring hydrographs have low peak flows and slow recessions during dry summers, and springs and groundwater-fed streams show little evidence of geomorphically effective incision. In the Cascades, drainage density increases linearly with time, accompanied by progressive hillslope steepening and valley incision. In watersheds >1 Ma, springs are absent and well-developed drainage networks fed by shallow subsurface flow produce flashy hydrographs with rapid summer recessions. A combination of mechanical, chemical, and biological processes acting within and on top of lava flows may reduce permeability over time, forcing flowpaths closer to the land surface. These shallow flowpaths produce flashy hydrographs with peakflows capable of sediment transport and landscape dissection. From these observations, I infer that the geomorphic evolution of basalt landscapes is dependent on their evolution from deep to shallow flowpaths.

People just keep publishing interesting stuff.

Fiorillo, F. 2009. Spring hydrographs as indicators of droughts in a karst environment. Journal of Hydrology 373: 290-301.

Rosenberry, D.O. and J. Pitlick. 2009. Effects of sediment transport and seepage direction on hydraulic properties at the sediment–water interface of hyporheic settings. Journal of Hydrology 373: 377-391.

Gresswell, R. et al. 2009. The design and application of an inexpensive pressure monitoring system for shallow water level measurement, tensiometry and piezometry. Journal of Hydrology 373: 416-425.

Fryar, A.E. 2009. Springs and the Origin of Bourbon [Historical Note], Ground Water, 47(4): 605-610.

Cardenas, M. Bayani. 2009. Stream-aquifer interactions and hyporheic exchange in gaining and losing sinuous streams Water Resour. Res., Vol. 45, No. 6, W06429

Selker, John; Ferre, Ty P. A. 2009. The ah ha moment of measurement: Introduction to the special section on Hydrologic Measurement Methods Water Resour. Res., Vol. 45, No. null, W00D00

Hodgkins, Glenn A. 2009. Streamflow changes in Alaska between the cool phase (1947-1976) and the warm phase (1977-2006) of the Pacific Decadal Oscillation: The influence of glaciers Water Resour. Res., Vol. 45, No. 6, W06502

Matott, L. Shawn; Babendreier, Justin E.; Purucker, S. Thomas Evaluating uncertainty in integrated environmental models: A review of concepts and tools Water Resour. Res., Vol. 45, No. 6, W06421

Orr, Cailin H.; Clark, Jeffery J.; Wilcock, Peter R.; Finlay, Jacques C.; Doyle, Martin W. Comparison of morphological and biological control of exchange with transient storage zones in a field-scale flume J. Geophys. Res., Vol. 114, No. G2, G02019

Katsuyama, Masanori; Kabeya, Naoki; Ohte, Nobuhito Elucidation of the relationship between geographic and time sources of stream water using a tracer approach in a headwater catchment Water Resour. Res., Vol. 45, No. 6, W06414

Phillips, J.D. 2009. Landscape evolution space and the relative importance of geomorphic processes and controls. Geomorphology, 109:79-85.

And last but not least:

Pretty much all of: Hydrological Processes, Special Issue: Hyporheic Hydrology: Interactions at the Groundwater-Surface Water Interface. Issue Edited by Stefan Krause, David M. Hannah, Jan H. Fleckenstein. Volume 23, Issue 15, 2009.

Most especially this article:
Boano, F., Revelli, R., and Ridolfi, L. 2009. Quantifying the impact of groundwater discharge on the surface-subsurface exchange, Hydrological Processes, 23(15): 2108-2116.

Megafloods from Glacial Lake Missoula

[Cross-posted at Highly Allochthonous]

If I had a time machine and could go back to any point in geologic history, as supposed in this month’s Accretionary Wedge call, the event I’d most like to see is the repeated flooding of the Pacific Northwest at the end of the last Ice Age. These “Missoula floods” are among the largest floods in Earth history and they irrevocably changed the topography of Washington and Oregon. My time machine would be an aircraft capable of flying with the floodwaters as they raced from Montana to the Pacific Ocean, and my time machine would also have LIDAR capabilities for collecting pre-, syn-, and post-flood digital measurements of topography and water surfaces and allowing an unparalleled determination of flood magnitudes and erosive volumes.

Our story begins shortly after the Last Glacial Maximum, deep in the heart of the Bitterroot Mountains in western Montana (Figure 1), as melt water from the waning glaciers began to pour into Clark Fork River valley and its tributaries. Water in the Clark Fork ponded up behind an enormous ice dam from a lobe of the Cordilleran Ice Sheet, and reached a maximum depth of 600 meters as Glacial Lake Missoula. The lake contained more than 2000 cubic kilometers of water, more than the modern volume of Lake Erie and Lake Ontario combined. Pedestrians in the modern day town of Missoula might notice a strange horizontal striping to the hillsides surrounding town (Figure 2)…these are the traces of the shorelines of the ancient lake.

Figure 1. USGS map of the Pacific Northwest between ~12 and 19 thousand years ago.

Figure 1. USGS map of the Pacific Northwest between ~12 and 19 thousand years ago.

Figure 2. Traces of Glacial Lake Missoula in Missoula, Montana, February 2009. Photo by the author.

Figure 2. Traces of Glacial Lake Missoula in Missoula, Montana, February 2009. Photo by the author.

After 19,000 years ago, water in Glacial Lake Missoula ruptured the ice dam, and the collected water went rushing downstream at speeds reaching 100 km/hr. Peak discharge in the Spokane Valley has been estimated at 17 +/- 3 million cubic meters per second, and drainage of the lake lasted several days.

Today, the Clark Fork River drains into the upper Columbia River and then into the Pacific Ocean. At the time of the Missoula Floods, the upper Columbia was buried under glaciers and that route was blocked to the floodwaters from Glacial Lake Missoula, so instead they were forced to take an overland route, carving new channels into the fertile Palouse loess deposits and underlying 17 Ma Columbia River basalts of eastern Washington. These channels are spectacular (Figures 3 and 4), up to 182 m deep and 32 km wide, with dry waterfalls, scoured potholes, and streamlined islands. Granite boulders the size of small cars were carried by the flood from the Idaho batholith and deposited in central Washington. Even for geologists, it can be hard to appreciate the full extent of these floods from the ground, but satellite photos (Figure 5) show the huge aerial extent of the erosion, covering a region we now call the Channeled Scablands.

Figure 3. Dry Falls and Grand Coulee near Coulee City, Washington, June 2004. The falls are 122 m high and 5.6 km wide. Photo by the author.

Figure 3. Dry Falls and Grand Coulee near Coulee City, Washington, June 2004. The falls are 122 m high and 5.6 km wide. Photo by the author.

Figure 4. Grand  Coulee downstream of Dry Falls as viewed from Lenore Caves, June 2004. Photo by the author.

Figure 4. Grand Coulee downstream of Dry Falls as viewed from Lenore Caves, June 2004. Photo by the author.

Figure 5. Landsat view of the Channeled Scablands region. This image was taken on August 31, 1972 and shows about 34,250 square kilometers of eastern Washington. The dark green features are the channels, the light green is the wheat-farmed Palouse region and the modern Columbia River is at the top right. Image retrieved from a<a href=Several times along their way across Washington, the floodwaters found basins in which to spread out and slow down. The fertile, wine-growing soils of the Yakima and Walla Walla valleys are slackwater flood deposits of loess from the Palouse valley. In a few special places, we can see the thick layers of silt, separated by thin horizons of soil (Figure 6). The number of layers preserved in these places help constrain the number of floods, and ash layers in the soils help constrain their timing. The best estimate is that there were more than 40 late Pleistocene megafloods that crossed eastern Washington, though not all of them may have come from from Glacial Lake Missoula itself. The floods began after 19 thousand years ago, many occur after 15 thousand years ago, and some post-date a Mount Saint Helens eruption 13 thousand years ago. More than 25 floods had peak discharges exceeding 1 million cubic meters per second.

Figure 6. Missoula flood deposits in the Walla Walley valley, Washington, June 2004. Photo by the author.

Figure 6. Missoula flood deposits in the Walla Walley valley, Washington, June 2004. Photo by the author.

Where the Columbia River turns east and runs along the modern-day border of Oregon and Washington, the Missoula Floods were once again confined to a single channel, at a place called Wallula Gap. As immense as the Columbia River Gorge is (Figure 7), this channel was a major constriction on the flood, only able to transmit 20% of the peak discharge. The waters back up behind the gap, flooding the Pasco Basin and creating temporary Lake Lewis around the tri-cities region of Washington. Floodwaters in the gorge were more than 215 m deep, as evidenced by the flood deposits found on surrounding ridgelines. The town of Lyle, Washington, in the Columbia River is built on a giant eddy bar left by the floods (Figure 7).

Figure 6. Columbia River Gorge, looking upstream from Rowena Crest, Oregon, June 2004. Photo by the author.

Figure 6. Columbia River Gorge, looking upstream from Rowena Crest, Oregon, June 2004. Photo by the author.

Figure 7. Lyle, Washington, as viewed from Rowena Crest, Orego. Photo by the author in June 2004.

Figure 7. Lyle, Washington, as viewed from Rowena Crest, Orego. Photo by the author in June 2004.

When the floods reached Portland, Oregon, the waters filled the Willamette Valley and turned into a lake 100 m deep, ~50 km wide, and 175 km long. Today the lake bottom is seen in the flat topography and fertile soils of the valley. Icebergs, probably remnants of the glacier that dammed Lake Missoula, were carried this far, because the valley is pocked by glacial erratics (Figure 8), rocks that had fallen onto or into the ice, were rafted downstream, and left behind when the icebergs melted. These rocks are not rounded, so it is clear that they did not as material moved by the flood itself.

Figure 8. Glacial erratic on the edge of the Willamette Valley in Erratic Rock State Park, Oregon. Photo taken May 2008 by <a href=Slowly the water would drain from the Willamette Valley and upstream lakes and empty completely into the Pacific Ocean through the Columbia River. Vegetation would encroach on the new sediments, and soil would begin to develop. In the meantime, another Glacial Lake Missoula would be forming behind a new ice dam on the Clark Fork River, getting ready to repeat the process again. Presumably floods of varying magnitudes continued until the glaciers had retreated north of the river. The last floods probably occurred less than 13 thousand years ago.

Floods over, measurements completed, my time machine and I would return to the present, ready to fill in the details of the floods that shaped the topography, soils, and agriculture of the Pacific Northwest. Even without a time machine, there’s so much more I could tell you about the Missoula Floods, but I’ve already gone on long enough. Instead I’ll refer you to the numerous scientific papers on the subject beginning with those of J. Harlan Bretz in the 1920s. When Bretz proposed a megaflood as the source of the Channeled Scablands, it flew in the face of the ruling uniformitarianism paradigm and his work was not accepted for several decades. The casual audience may want to check out the Ice Age Floods Institute website, an on-line USGS publication on the The Channeled Scablands of Eastern Washington, the book Cataclysms on the Columbia, and, if you can find it airing sometime, the excellent Oregon Public Broadcasting documentary Ice Age Floods. If you live in or are traveling to the Pacific Northwest, also keep an eye out for sites along the newly-approved Ice Age Floods National Geologic Trail.

AGU Abstract Submitted: Secular Streamflow Trends in Watersheds Receiving Mixed Rain and Snow, Pacific Coast and Cascades Ranges

The following abstract was submitted for the Fall AGU meeting:

Secular Streamflow Trends in Watersheds Receiving Mixed Rain and Snow, Pacific Coast and Cascades Ranges

A. Jefferson, University of North Carolina at Charlotte

Much existing research has focused on detecting climate change effects on snowmelt-dominated watersheds, but in the Pacific Coast and Cascades ranges, precipitation falls as either rain or snow, depending on latitude, elevation, and season. Watersheds often straddle the snow line, with some areas dominantly receiving rain and higher elevations accumulating seasonal snowpacks. These snowpacks are near the 0°C threshold, making them sensitive to the effects of climate warming. Climate sensitivity of seasonal and event hydrographs from watersheds with mixed rain and snow has not been fully explored. This project investigates detectable climate change signals in long-term streamflow records in the Washington, Oregon, and northern California Coast and Cascades Ranges.

Watersheds with mean elevations above the seasonal snow line show significant increases in streamflow during January through March and decreases in the percent of annual flow during April through June, the historical snowmelt period. These changes were not detectable in watersheds with mean elevations below the seasonal snow line. There were no consistent trends in peakflow dates or volumes. The multiple drivers of peakflow occurrence make it unlikely that any changes in peakflow timing will be detectable for several decades. Results suggest that Coast Range hydrology has been minimally impacted by historical climate warming, but that Cascades Range watersheds are already experiencing altered hydrologic regimes.

Pending acceptance, the work will be presented in session H32 Spatial and Temporal Trends in Hydrometeorological Records as Indicators of Climate Variability and Change.