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EGU Abstract: Potential impact of lava flows on regional water supplies: case study of central Oregon Cascades volcanism and the Willamette Valley, USA

This abstract was just submitted to the European Geosciences Union meeting for a session on “NH9.9. Natural hazard impact on technological systems and urban areas.” I won’t get to go to Vienna in April, but at least a little bit of my science will. Thanks to Natalia for finding a graceful way to integrate our work.

Potential impact of lava flows on regional water supplies: case study of central Oregon Cascades volcanism and the Willamette Valley, USA

Natalia I. Deligne, Katharine V. Cashman, Gordon E. Grant, Anne Jefferson

Lava flows are often considered to be natural hazards with localized bimodal impact – they completely destroy everything in their path, but apart from the occasional forest fire, cause little or no damage outside their immediate footprint. However, in certain settings, lava flows can have surprising far reaching impacts with the potential to cause serious problems in distant urban areas. Here we present results from a study of the interaction between lava flows and surface water in the central Oregon Cascades, USA, where we find that lava flows in the High Cascades have the potential to cause considerable water shortages in Eugene, Oregon (Oregon’s second largest metropolitan area) and the greater Willamette Valley (home to ~70% of Oregon’s population). The High Cascades host a groundwater dominated hydrological regime with water residence times on the order of years. Due to the steady output of groundwater, rivers sourced in the High Cascades are a critical water resource for Oregon, particularly in August and September when it has not rained for several months. One such river, the McKenzie River, is the sole source of drinking water for Eugene, Oregon, and prior to the installation of dams in the 1960s accounted for ~40% of river flow in the Willamette River in Portland, 445 river km downstream of the source of the McKenzie River. The McKenzie River has been dammed at least twice by lava flows during the Holocene; depending the time of year that these eruptions occurred, we project that available water would have decreased by 20% in present-day Eugene, Oregon, for days to weeks at a time. Given the importance of the McKenzie River and its location on the margin of an active volcanic area, we expect that future volcanic eruptions could likewise impact water supplies in Eugene and the greater Willamette Valley. As such, the urban center of Eugene, Oregon, and also the greater Willamette Valley, is vulnerable to the most benign of volcanic hazards, lava flows, located over 100 km away.

Abstract: Timescales of drainage network evolution are driven by coupled changes in landscape properties and hydrologic response

I will be at the CUAHSI 3rd Biennial Colloquium on Hydrologic Science and Engineering on July 16-18, 2012 in Boulder, Colorado. I’ve been asked to speak in a session on the co-evolution of geomorphology and hydrology. This is a cool opportunity for me, as I’ve been thinking about co-evolution in both volcanic landscapes and Piedmont gullies for the past couple of years. I’m going to attempt to stitch those two very different landscapes and timescales together in one conceptual framework in the talk, and I guess we’ll see how it goes.

Timescales of drainage network evolution are driven by coupled changes in landscape properties and hydrologic response
Anne J. Jefferson

In diverse landscapes, channel initiation locations move up or downslope over time in response to changes in land surface properties (vegetation, soils, and topography) which control the partitioning of water between subsurface, overland, and channelized flowpaths. In turn, channelized flow exerts greater erosive power than overland or subsurface flows, and can much more efficiently denude and dissect the landscape, leading to altered flowpaths and land surface properties. These feedbacks can be considered a fundamental aspect of catchment coevolution, with the headward extent of the stream network and landscape dissection as prime indicators of the evolutionary status of a landscape.

Photo by Ralph McGee, used with Permission.

Gullying in a Piedmont forest, downslope from a pasture. Cabin Creek headwaters, Redlair. Photo by Ralph McGee, used with permission.

Drainage network evolution in response to landscape change may occur over multiple timescales, depending on the rapidity of change in the hydrogeomorphic drivers. Climate and lithology may also modify the rates at which drainage networks respond to change in land surface properties. On basaltic landscapes, such as the Oregon Cascades, timescales of a million years or more can be necessary to evolve from an undissected landscape with slow, deep groundwater drainage to a fully-dissected landscape dominated by shallow subsurface stormflow and rapid hydrograph response in streams. This evolution seems to be driven by a slow change in land surface properties and permeability as a result of weathering, soil development, and mantling by low permeability materials, but may also reflect the high erosion resistance of crystalline bedrock. Conversely, rapid or near-instantaneous changes in land surface properties , such as accompanied the beginning of intensive agriculture in the southeastern Piedmont, can propagate into rapid (1-10 year) changes in channel network extent on clay-rich soils. Where agriculture has been abandoned in this region and forests have regrown, downslope retreat and infilling of extensive gully networks is occurring on decadal timescales.

Chapman Abstract: Top down or bottom up? Volcanic history, climate, and the hydrologic evolution of volcanic landscapes

In July 2011, Anne was a plenary speaker at the Chapman Conference on The Galápagos as a Laboratory for the Earth Sciences in Puerto Ayora, Galapágos. Anne was tasked with reviewing the state-of-knowledge of volcanic island hydrology and identifying pressing questions for future research in this 40 minute talk. The following is the abstract which she submitted when she began the task.

Top down or bottom up? Volcanic history, climate, and the hydrologic evolution of volcanic landscapes

Volcanic landscapes are well suited for observing changes in hydrologic processes over time, because they can be absolutely dated and island chains segregate surfaces of differing age. The hydrology of mafic volcanic landscapes evolves from recently emplaced lava flows with no surface drainage, toward extensive stream networks and deeply dissected topography. Groundwater, a significant component of the hydrologic system in young landscapes, may become less abundant over time. Drainage density, topography, and stream and groundwater discharge provide readily quantifiable measures of hydrologic and landscape evolution on volcanic chronosequences. In the Oregon Cascades, for example, the surface drainage network is created and becomes deeply incised over the same million-year timescale at which springs disappear from the landscape. But chronosequence studies are of limited value if they are not closely tied to the processes setting the initial conditions and driving hydrologic evolution over time.

Landscape dissection occurs primarily by erosion from overland flow, which is absent or limited in young, mafic landscapes. Thus, volcano hydrology requires conceptual models that explain landscape evolution in terms of processes which affect partitioning of water between surface and subsurface flows. Multiple conceptual models have been proposed to explain hydrologic partitioning and evolution of volcanic landscapes, invoking both bottom up (e.g., hydrothermal alteration) and top down processes (e.g., soil development). I suggest that hydrologic characteristics of volcanic islands and arcs are a function of two factors: volcanic history and climate. We have only begun to characterize the relative importance of these two drivers in setting the hydrologic characteristics of volcanic landscapes of varying age and geologic and climatic settings.

Detailed studies of individual volcanoes have identified dikes and sills as barriers to groundwater and lava flow contacts as preferential zones of groundwater movement. Erosion between eruptive episodes and deposits from multiple eruptive centers can complicate spatial patterns of groundwater flow, and hydrothermal alteration can reduce permeability, decreasing deep groundwater circulation over time. Size and abundance of tephra may be a major geologic determinant of groundwater/surface water partitioning, while flank collapse can introduce knickpoints that drive landscape dissection. The combination of these volcanic controls will set initial conditions for the hydrology and drive bottom up evolutionary processes.

Climatic forcing drives many top down processes, but understanding the relative effectiveness of these processes in propelling hydrologic evolution requires broader cross-site comparisons. The extent of weathering may be a major control on whether water infiltrates vertically or moves laterally, and we know weathering rates increase until precipitation exceeds evapotranspiration. Weathering by plant roots initially increases porosity, but accumulation of weathered materials, such as clays in soils, can reduce near-surface permeability and promote overland flow. Similarly, eolian or glacial inputs may create low permeability covers on volcanic landscapes.

View into the crater of Sierra Negra Volcano on Isabella Island, Galapagos

View of the 2005 lava inside the crater of Sierra Negra Volcano on Isabella Island, Galapagos. Photo by A. Jefferson

New publication: Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA

How does a landscape go from looking like this…

<2000 year old landscape on basaltic lava with no surface drainage

~1500 year old basaltic lava landscape with no surface drainage

to looking like this?

2 Million year old landscape on basaltic lava

2 Million year old landscape on basaltic lava. Note steep slopes and incised valleys

Find out in my new paper in Earth Surface Processes and Landforms.

Hint: Using a chronosequence of watersheds in the Oregon Cascades, we argue that the rates and processes of landscape evolution are driven by whether the water sinks into the lava flows and moves slowly toward springs with steady hydrographs or whether the water moves quickly through the shallow subsurface and creates streams with flashy hydrographs. Further, we suggest that this water routing is controlled by an elusive landscape-scale permeability which decreases over time as processes like chemical weathering create soil and clog up pores in the rock. And as a bonus, because of the high initial permeability of basaltic landscapes, the formation of stream networks and the dissection of the landscape appears to take far longer than in places with less permeable lithologies.

Jefferson, A., Grant, G., Lewis, S., & Lancaster, S. (2010). Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA Earth Surface Processes and Landforms, 35 (7), 803-816 DOI: 10.1002/esp.1976

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.

The hydrogeology of Yellowstone: It's all about the cold water

Cross posted at Highly Allochthonous

ResearchBlogging.orgThe Yellowstone caldera is home to thousands of geothermal springs and 75% of the world’s geysers, with kilometers-deep groundwater flow systems that tap magmatic heat sources. As that hot groundwater rises toward the surface, it interacts with shallower, cooler groundwater to produce multi-phase mixing, boiling, and a huge array of different hydrothermal features. While the deep, geothermal water is sexy and merits both the tourist and scientific attention given to it, there’s a largely untold story in the shallow groundwater, where huge volumes of cold water may advect more heat than the hydrothermal features.

Grand Prismatic Spring at Yellowstone National Park. Photo by Alaskan Dude on Flickr.
Grand Prismatic Spring. (Photo by Alaskan Dude on Flickr.)

Yellowstone is a rhyolitic caldera that has produced 6000 cubic kilometers of ash flow tuffs, rhyolites, and basalts that form a poorly-characterized, heterogeneous fractured rock aquifer, hosting both hot/deep and cold/shallow flow systems. The Yellowstone volcanics lie on top of the Rocky Mountain Cordillera, which itself is a complex hydrogeologic system, ranging from low permeability metamorphic rocks to high permeability limestones.

In a paper in the Journal of Hydrology, Gardner and colleagues (2010) use stream hydrographs and groundwater residence times to characterize the cold, shallow groundwater of the greater Yellowstone area. Stream hydrographs, or the time series of stream discharge, are useful indicators of groundwater dynamics, because in between rain or snowmelt events, streamwater is outflowing groundwater. The recession behavior of a hydrograph during periods between storms can be used to estimate aquifer volumes. In the Yellowstone region, the annual hydrograph is strongly dominated by the snowmelt peak, and Gardner et al. used the mean daily discharge record from 39 streams to characterize the recession behavior of streams on different lithologies. What they found was that streams flowing in watersheds dominated by volcanic rocks have much less variable hydrographs than those on other rock types. The figure below uses data from the USGS to illustrate these differences, which are in line with studies in the Oregon Cascades* and elsewhere which suggest that young volcanic rocks produce groundwater-fed streams with muted hydrographs.

Daily discharge for the Firehole River (USGS gage #06036905) and Soda Butte Creek (USGS gage #06187950) for the 2006-2007 water years, expressed on a unit area basis.

Using a nifty technique to separate the recessions into components attributable to snowmelt versus groundwater, Gardner et al. were able to calculate a ratio of the groundwater discharge to the total discharge of each stream and to calculate the hydraulic diffusivity, which is a ratio of permeability (how easily a fluid moves through a rock) compared to the amount of water stored in the system. If hydraulic diffusivity is low, the flow in the stream decreases slowly over time, like the Firestone River in the figure above. But hydraulic diffusivity can be low either because of low permeability or large aquifer storage volumes, so being able to tease apart those two components is key to understanding the hydrograph behavior. Gardner et al. did this by looking at the ratio of groundwater discharge to maximum discharge and using that as an index of aquifer storage. Based on these ratios, Gardner et al. separated the streams in the Yellowstone area into three groups (runoff-dominated, intermediate, and groundwater-dominated) with contrasting hydrogeologic properties.

Upper Cenozoic Geologic Map, Yellowstone Plateau
Geologic map of a portion of the Yellowstone Plateau, with approximate locations of stream gages of interest noted. Modified from Christiansen (2001, USGS Prof. Pap. 729-G).

Soda Butte and Teton Creeks are runoff dominated, with low groundwater storage and middling recession behavior. Since there is little groundwater storage, in order for hydraulic diffusivity to be low, then permeability must also be low. Sure enough, Teton Creek lies on top of Precambrian gneiss and granite, and unfractured metamorphic and intrusive igneous rocks like these have the lowest possible permeabilities. The Soda Butte Creek watershed comprises Eocene Absaroka volcanics, and older volcanic rocks like these can be quite weathered to clays and relatively impermeable.

The intermediate watersheds of Tower Creek and Cache Creek have significant ratios of groundwater discharge to maximum discharge, but their hydrographs recede rapidly over the summer. This means that they have high permeabilities relative to their aquifer storage volume. The Tower Creek watershed has Eocene tuffs and glacial valleys with alluvial fill, and Cache Creek watershed has Paleozoic carbonates. These materials are known for their high permeabilities, and the low storage volumes can be explained if those layers thinly overly less conductive materials.

The Firehole River, Gibbon River, and Snake River above Jackson Lake are groundwater-dominated, with very high permeabilities but even larger aquifer storage volumes. All of those streams drain primarily Quaternary Yellowstone volcanics, and this hydrologic behavior is in keeping with other young volcanic terrains.

Not content to stop with this hydrogeologic classification of the Yellowstone area, Gardner et al. collected water samples from small, cold springs to analyze CFC and tritium concentrations, which are useful tracers of groundwater travel times. For the springs they sampled, they found an average travel time (from recharge to discharge) of ~30 years. Using those CFC-derived groundwater transit times and some back-of-the-envelope estimates of aquifer geometry, Gardner et al. estimate that the Quaternary Yellowstone volcanics have a permeability of 10-11 to 10-13 m2, which is in line with estimates of young volcanics elsewhere. They also estimated that the aquifer depth represented by these small springs was ~70 m, but speculated that deeper flowpaths might have been discharging directly into the streams, out of reach of their CFC and tritium sampling abilities.

Finally, Gardner et al. note that the cold springs they studied are actually not as cold as they should be. In fact, they appear to be what are coming to be called “slightly thermal” springs. Groundwater recharge temperature is commonly assumed to be approximately mean annual temperature, and in the Norris Geyser Basin area, that’s around 4-5 &deg C. But the cold springs in the area are around 10 &deg C. Using this temperature difference and a handy equation from Manga and Kirchner (2004), Gardner et al. are able to calculate the heat flux advected by these cool springs. Their value of ~3800 W/m2 for the springs around Norris is about 10% of the heat flux from the Norris and Gibbon Geyser Basins themselves. That number becomes even more astonishing when you consider the relative scales of the cool versus the thermal groundwater systems. Geyser basins cover ~10 km2 of the Yellowstone Plateau, whereas cool groundwater drains under the entire ~1000 km2 plateau, and could be discharging far more heat than those showy thermal springs and geysers themselves.

So if you happen to go to Yellowstone this summer, in between gawking at Old Faithful, Artist Paint Pots, and Mammoth Hot Springs, take a few moments to appreciate the waters of the less dramatic cool rivers and streams. Their waters too are profoundly shaped by the geologic history of Yellowstone, and they are taking an awful lot of heat.

*Disclaimer: My PhD research focused on the hydrology and hydrogeology of volcanic aquifers and streams of the Oregon Cascades.

Payton Gardner, W., Susong, D., Kip Solomon, D., & Heasler, H. (2010). Snowmelt hydrograph interpretation: Revealing watershed scale hydrologic characteristics of the Yellowstone volcanic plateau Journal of Hydrology, 383 (3-4), 209-222 DOI: 10.1016/j.jhydrol.2009.12.037

The Hydrology and Evolution of Basaltic Landscapes: Notes from GSA Sunday

This post is cross-posted at Highly Allochthonous. Please look over there for any comments.

Like many North American geobloggers, I’ve recently returned from the Geological Society of America meeting in Portland, Oregon. It was a bittersweet trip for me, as it was a return to my spiritual homeland, where I spent five happy years working on the rocks and waters of the Cascade Range. Since then, I’ve felt a bit exiled on the Eastern Seaboard, so it was perhaps apropos that the trip back was a bit of a tease…in my four days in Oregon, I did not manage to see a single mountain. The picture to the right is the Hood River, draining the north side of Mt. Hood, about 45 minutes east of Portland. It was taken in April 2007, during field work for my post-doc.


After an unexpectedly long layover in Phoenix and an entirely unexpected layover in San Francisco (thank you, US Airways), I arrived in Portland at 1 am local time Sunday morning. With any potential time-change/jet-lag problems thus mitigated, I arrived bright eyed for the first talks on Sunday morning.

The main order of business on Sunday morning was the Pardee Keynote Symposium on “The Evolution of Basaltic Landscapes: Time and River and the Lava Flowing.” I arrived in time to hear a fascinating talk on “Impacts of basaltic volcanism on incised fluvial systems: does the river give a dam?” by blogger/tweep/mapper extraordinaire Kyle House. He was talking about the lava dams, debris flows, and river incision of the Owyhee River of eastern Oregon. After a few gorgeous photos accompanied magnificent Lidar images, I was thoroughly convinced of the utility of Lidar for high-resolution geological mapping. I was also salivating at the thought of a whole day of water + lava talks full of gorgeous volcano photos.

After Steve Ingebritsen gave a lovely overview of the hydrogeology of basalts, Dennis Geist convinced me that I absolutely have to go to the Galapagos Islands, by showing pictures of volcanoes with whales for scale. His talk focused on the connections between geology and biology in the Galapagos, and got me thinking about the implications of volcanic emergence and subsidence for the evolution of the creatures of the famous archipelago. While Geist tried to convince his audience that the vegetation of the Galapagos is supported with basically no soil, neither I nor the next speaker, Oliver Chadwick, quite believed him on that point.

Indeed Chadwick talked about the patterns and processes of soil development on basaltic landscapes, where weathering rates depend not only on the usual climatic factors but also on the flow texture – with aa and pahoehoe flows exhibitting different patterns and timescales of soil development. For my own work, one key point that Chadwick made was “At some point in the history of lava flows, the surface becomes less permeable than the whole…” I think that statement has implications for the way we think about drainage development in basaltic landscapes, but I’ll wait to say more about that until my publication and/or funding record bear me out.

I spent my afternoon thinking more about basalt hydrology, in a session on “Hydrologic Characterization and Simulation of Neogene Volcanic Terranes.” I’ve got lots of notes from that session that are probably of interest only to me, but I will say that it was exciting to hear one of the grad student speakers say to me “I’ve been reading your dissertation” and to hear my work cited more than once. It is such a relief to know that people working in the field actually find my work interesting or useful. Towards the end of the session, I gave a talk on the geomorphic and hydrologic co-evolution of the central Oregon Cascades Range. My talk was based on a paper that has undergone several major revisions since my Ph.D. days, and it was a pleasure to share the latest and greatest incarnation of my thinking on the subject. The pleasure was immeasurably increased by a recent letter from the journal editor giving me only very minor revisions to do before acceptance.

On Sunday evening, the attendees of the morning talks reconvened for a wine tasting with a geological theme – the terroir of taste of Oregon wines grown on basalt versus sandstone. The wine was donated by Willamette Valley Vineyards (basalt) and King Estate (sandstone), and we got to hear from the wine makers as we sipped their wares. According to them, if you see a 2008 Willamette Valley appellation Pinot Noir or Pinot Gris, snap it up. They reckon it will be the best year ever for Oregon wines. That’s saying quite a bit, since Oregon is consistently recognized as one of the world’s best Pinot producing regions.

After a day of stimulating talks and invigorating conversation, I was ready to dive into two days focused on groundwater-surface water interactions and a day of snow, mega-floods, and debris flows to round out my conference. But my notes on those days will have to wait for now, as those paper revisions are not taking care of themselves.

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.

Redoubt erupts and we can watch safely from the web

Though born and raised in the craton of North America, my PhD field work looked at the interplay between volcanism, hydrology, and geomorphology in the Oregon Cascades. I’ll admit that I’ve become a bit of a volcano geek, and the last few weeks have provided some really spectacular eruptions to watch safely from my non-volcanically active perch in North Carolina.

First up, we had the undersea eruption and emergence of a new island near Tonga. Intrepid locals and airline passengers snapped some amazing pictures, best showcased on the Boston Globe’s Big Picture site. The eruption was a textbook example of a Surtseyan eruption, well, if Surtsey itself hadn’t already coined the phrase.

Just when we thought it would never happen, Alaska’s Redoubt Volcano decided to put on a good show for us. The eruption started on March 22nd, but the biggest eruption so far occurred this morning at 9:24 am Alaska time. The ash column reached 20 km into the atmosphere.  Images of the volcano also show new lahar deposits going down the Drift River valley.

One of the cool features of these eruptions has been the ability of even armchair volcano enthusiasts to watch the events unfold in near real-time. The Alaska Volcano Observatory (AVO) has a webcam with a nice view of Redoubt’s summit (image below is from this evening), you can follow the course of the eruption on AVO’s twitter feed,  and there are some excellent volcano-centric bloggers who are doing a commendable job  of providing commentary on the eruptions. Of the volcano bloggers, I’d have to say my favorite is Erik Klemetti of Eruptions. Erik is an igneous petrologist, and a fellow OSU Geosciences alum.

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View of Redoubt from AVO’s Hut webcam as of 26 March 2009, 17:50 Alaska Daylight Time.