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When it rains a lot and the mountains fall down

Cross-posted at Highly Allochthonous

2006 debris flow deposit in the Eliot Glacier drainage, north flank of Mount Hood (Photo by Anne Jefferson)

The geo-image bonanza of this month’s Accretionary Wedge gives me a good reason to make good on a promise I made a few months ago. I promised to write about what can happen on the flanks of Pacific Northwest volcanoes when a warm, heavy rainfall hits glacial ice at the end of a long melt season. The image above shows the result…warm heavy rainfall + glaciers + steep mountain flanks + exposed unconsolidated sediments are a recipe for debris flows in the Cascades. Let me tell you the story of this one.

It was the first week of November 2006, and a “pineapple express” (warm, wet air from the tropic Pacific) had moved into the Pacific Northwest. This warm front increased temperatures and brought rain to the Cascades…a lot of rain. In the vicinity of Mt. Hood, there was more than 34 cm in 6 days, and that’s at elevations where we have rain gages. Higher on the mountain, there may even have been more rain…and because it was warm, it was *all* rain. Normally, at this time of year, the high mountain areas would only get snow.

While it was raining, my collaborators and I were sitting in our cozy, dry offices in Corvallis, planning a really cool project to look at the impact of climate change on glacial meltwater contributions to the agriculturally-important Hood River valley. Outside, nature was opting to make our on-next field season a bit more tricky. We planned to install stream gages at the toe of the Eliot and Coe glaciers on the north flank of Mt. Hood, as well as farther downstream where water is diverted for irrigation. But instead of nice, neat, stable stream channels, when we went out to scout field sites the following spring, we were greeted by scenes like the one above.

Because sometime on 6 or 7 November, the mountain flank below Eliot Glacier gave way…triggering a massive debris flow that roared down Eliot Creek, bulking up with sediment along the way and completely obliterating any signs of the pre-existing stream channel. By the time the flow reached the area where the irrigation diversion occur, it had traveled 7 km in length and 1000 m in elevation, and it had finally reached the point where the valley opens up and the slope decreases. So the sediment began to drop out. And debris flows can carry some big stuff (like the picture below) and like the bridge that was washed out, carried downstream 100 m and turned sideways.

2006 Eliot Glacier debris flow deposit (photo by Anne Jefferson)

2006 Eliot Glacier debris flow deposit (photo by Anne Jefferson)

In this area, the deposit is at least 300 m wide and at least a few meters deep.

Eliot Creek, April 2007 (photo by Anne Jefferson)

Eliot Creek, April 2007 (photo by Anne Jefferson)

With all the big debris settling out, farther downstream the river was content to just flood…

Youtube video from dankleinsmith of the Hood River flooding at the Farmers Irrigation Headgates

and flood…

West Fork Hood River flood, November 2006 from

West Fork Hood River flood, November 2006 from For the same view during normal flows, take a look at my picture from April 2007:

and create a new delta where Hood River enters the Columbia.

Hood River delta created in November 2006 (photo found at

Hood River delta created in November 2006 (photo found at

And it wasn’t just Mt. Hood’s Eliot Glacier drainage that took a beating in this event. Of the 11 drainages on Mt. Hood, seven experienced debris flows, including a rather spectacular one at White River that closed the main access to a popular ski resort. And every major volcano from Mt. Jefferson to Mt. Rainier experienced debris flows, with repercussions ranging from downstream turbidity affecting the water supply for the city of Salem to the destruction of popular trails, roads, and campgrounds in Mt. Rainier National Park (pdf, but very cool photos).

In the end, our project on climate change and glacial meltwater was funded, we managed to collect some neat data in the Eliot and Coe watersheds in the summer of 2007, and the resulting paper is wending its way through review. The November 2006 debris flows triggered at least two MS thesis projects and some serious public attention to debris flow hazards in the Pacific Northwest. They also gave me some really cool pictures.

Delta upon Delta

For some reason the last few days have seen me browsing the semi-frozen areas of the Earth and in my search for the perfect thermokarst landscape, I’ve run across some really nice deltas. I don’t know anything about the one below other than its location in far northwestern Saskatchewan, but it looks to me like this river had built a beautiful fan delta only to see the lake shoreline dramatically change (perhaps as a result of isostatic rebound?) triggering the building of not one, but two, new fan deltas like Mickey Mouse ears on the margins of the old one.

The image below is from Google Earth. Here’s the Flash Earth permanent link:…

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Deltas into Rivers: Chippewa River into the Mississippi River, Wisconsin

The Chippewa River drains the glaciated terrains of north-central Wisconsin including major outwash plains from the margins of the Laurentide Ice Sheet.  The sand carried by the Chippewa is a major sediment source for the Upper Mississippi River for tens of miles downstream.  The Chippewa forms a beautiful delta into the Mississppi River, as seen below, creating the only natural lake on the Mississippi, in the form of Lake Pepin (birthplace of water-skiing, by the way).  I like this delta because we don’t often think of riverine deltas forming in the rivers, and their propogating upstream and downstream effects. Plus, it makes a pretty contrast to the dissected blufflands of the Driftless area.

Flash earth link: If you zoom in on Flash Earth you can get some nice imagery of the sand bars and fluvial islands of the Chippewa as you move upstream, plus some nice long anastomosing reaches.

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The pathologically curvy Rio Grande Delta

I spent a summer in college staring at maps and aerial photographs of the Rio Grande delta in Texas and Mexico. Maybe now I can get some use out of it.  I was working with J.D.  Stanley at the Smithsonian’s NMNH and he pointed me to the apparently high sinuosity of deltaic channels on the Texas side of the Rio Grande delta.

According to my notes, the modern Rio Grande has a sinuosity of 2.075 in its delta, while Holocene channels have a sinuosity of 1.83, younger Pleistocene channels have a sinuosity of 1.81 and remnants of older Pleistocene channels have about 1.32. So our data suggests that the channels of the Rio Grande delta have gotten curvier over time. I also did a literature review of channel sinuosity in other deltas and found that the Rio Grande was indeed anomalously sinuous compared to many of the world’s major deltas.  In my review, only the Niger and Klangat Langat deltas were curvier. Unfortunately, we never came up with a good mechanism to explain why the Rio Grande was so curvaceous.

Indeed, if you look at the flash earth images (  below, you can see what caught our eye. One of the images is the majority of the delta (look for the anthropogenically straightened main outlet channel), one zooms in on the modern river mouth and area just to the north, one shows a portion of the southern, Mexico portion of the delta, and one shows the northern portion of the delta, which if I recall correctly has some of the oldest exposed deltaic deposits along with some eolian features (which can been seen in the image).

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Bombetoka Bay, Madagascar

Hunting for a Where on Google Earth location a while ago I ran across this wonderful tidally-influenced delta on the northwest coast of Madagascar. It is the mouth of the Betsiboka River and just north of the river mouth is the second largest port in Madagascar.

What struck me about the delta was not just the nice tug-of-war between riverine and tidal processes in shaping the islands, but the dramatic red color of the water in the Google Earth image (and others as well). This red color is symptomatic of the massive erosion resulting from rampant deforestation of the island.

The four photos are from Flash Earth, Google Earth, and the Gateway to Astronaut Photography, NASA Earth Observatory (ASTER satellite)

Flash earth permanent link:

Astronaut Photograph:

Earth Observatory ASTER image:

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