Currently browsing tag


How low will they go? The response of headwater streams in the Oregon Cascades to the 2015 drought

From a distance, Anne has been watching an incredibly unusual summer play out in the Pacific Northwest, following a winter with far less snow (but more rain) than usual. Folks on the ground in Oregon have been collecting data on the response of the Oregon Cascades streams to “no snow, low flow” conditions. Anne is making minor contributions to the following poster, to be presented in Session No. 291, Geomorphology and Quaternary Geology (Posters) at Booth# 101 on Wednesday, 4 November 2015: 9:00 AM-6:30 PM.


LEWIS, Sarah L.1, GRANT, Gordon E.2, NOLIN, Anne W.1, HEMPEL, Laura A.1, JEFFERSON, Anne J.3 and SELKER, John S.4, (1)College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, (2)Pacific Northwest Research Station, USDA Forest Service, 3200 SW Jefferson Way, Corvallis, OR 97331-8550, (3)Department of Geology, Kent State University, Kent, OH 44242, (4)Biological & Ecological Engineering, Oregon State University, Corvallis, OR 97331,

Larger rivers draining the Oregon Cascades are sourced from headwater systems with two distinct runoff regimes: surface-flow dominated watersheds with flashy hydrographs, rapid baseflow recession, and very low summer flows; and spring-fed systems, with slow-responding hydrographs, long baseflow recession, and summer flow sustained by deep groundwater fed coldwater springs. Our previous research has explored these differences on both the wet west-side and dry east-side of the Cascade crest, as expressed in contrasting discharge and temperature regimes, drainage efficiency, low and peak flow dynamics, and sensitivity to snowpack and climate change scenarios. In 2015, record low winter snowpack combined with an anomalously dry spring resulted in historically low flows across our research sites and throughout Oregon. These extreme meteorological conditions, equivalent to a 4°C warming scenario, offer an exceptional opportunity to witness how these contrasting stream networks might respond to anticipated changes in amount and timing of recharge.
Conceptually, channel network response to decreasing discharge may involve both lateral and longitudinal contraction. Lateral contraction, the decrease of wetted channel width and depth, occurs in both surface-flow and spring-fed streams as flows diminish. Longitudinal contraction may be expressed as (a) a gradual drying of the stream channel and downstream retreat of the channel head, (b) a “jump” of the channel head downstream to the next spring when an upper spring goes dry, or (c) no change in channel head despite diminishing flows. We hypothesize that while individual stream channels may display a combination of these dynamics, surface-flow and spring-fed watersheds will have distinctive and different behaviors. We field test our hypothesis by monitoring channel head locations in 6 watersheds during the low flow recession of 2015, and repeatedly measuring discharge, water quality and hydraulic geometry at a longitudinal array of sites along each surface-flow or spring-fed channel. The resulting data set can be used to explore the fundamental processes by which drainage networks accommodate decreasing flows.

New paper: Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions

Snowline near Skykomish, Washington (photo on Flickr by RoguePoet, used under Creative Commons)

Snowline near Skykomish, Washington (photo on Flickr by RoguePoet, used under Creative Commons)

Jefferson, A. 2011. Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions, Geophysical Research Letters, 38, L16402, doi:10.1029/2011GL048346.


In maritime mountainous regions, the phase of winter precipitation is elevation dependent, and in watersheds receiving both rain and snow, hydrologic impacts of climate change are less straightforward than in snowmelt-dominated systems. Here, 29 Pacific Northwest watersheds illustrate how distribution of seasonal snow, transient snow, and winter rain mediates sensitivity to 20th century warming. Watersheds with >50% of their area in the seasonal snow zone had significant (? ? 0.1) trends towards greater winter and lower summer discharge, while lower elevations had no consistent trends. In seasonal snow-dominated watersheds, runoff occurs 22–27 days earlier and minimum flows are 5–9% lower than in 1962, based on Sen’s slope over the period. Trends in peak streamflow depend on whether watershed area susceptible to rain-on-snow events is increasing or decreasing. Delineation of elevation-dependent snow zones identifies climate sensitivity of maritime mountainous watersheds and enables planning for water and ecosystem impacts of climate change.

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.

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.

Cascades hydrogeology on front page of the Oregonian

The front page feature of today’s Oregonian (Portland’s major newspaper) features research on groundwater in the Cascades: The secret’s out: Tons of water in Oregon’s Cascades.

Scientists from the U.S. Forest Service and Oregon State University have in recent years quietly realized that the high Cascades in Oregon and far Northern California contain an immense subterranean reservoir about as large as the biggest man-made reservoirs in the country.

The secret stockpile stores close to seven years’ worth of Oregon rain and snow and is likely to become increasingly precious, even priceless, as population and climate add pressure to water supplies.

The reservoir hides within young volcanic rock — less than 1 million years old — in the highest reaches of the Cascades. The rock is so full of cracks and fissures it forms a kind of vast geological sponge. Heavy rain and snow falling on the rock percolate into the sponge, like a river filling a reservoir.

“It’s not just the fact we get a lot of rain in Oregon that gives us copious amounts of water,” says Gordon Grant, a research hydrologist at the U.S. Forest Service’s Pacific Northwest Research Station leading the research. “It’s the unique geology — the plumbing system — that allows us to retain much of it.”

Much of the work summarized in the article was associated with my Ph.D. research. For some of the details, you can read here and here. For a more complete list of related publications, see here.