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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.

yellowstone-hydrograph.jpg
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

A selected few Eyjafjallajokull links

The eruption of Eyjafjallajokull (which means Island Mountain Glacier in Icelandic) started out in March as a relatively quiet and tourist-friendly Hawaiian style eruption. That petered out and then a few days later, the magma reemerged subglacially, producing the spectacular ash-producing phreato-magmatic eruption that has transfixed the world and stranded all would-be European air passengers. The Boston Globe’s Big Picture coverage has been as-usual spectacular. Check out these two photo sets (15 April, 19 April). NASA’s Earth Observatory has also been producing some nice images of the ash plume. Follow them here.

And few days into the eruption, the magmatic heat produced enough glacier melt not just to fuel the ash production but also to generate an outburst flood, as captured on video below:
[youtube=http://www.youtube.com/watch?v=9sryalI57oo&feature=player_embedded]

The video above includes a rather spectacular train of standing waves, which led to some debate amongst some friends and I over whether they represented sub- or super-critical flow. Fortunately, I have access to an expert on the subject, Gordon Grant, who weighed in thusly:

The standing waves represent what is best referred to as “trans-critical flow”, that is flow that oscillates around Froude No. = 1. We have real-time (though very small scale compared to what you’re seeing in the video) measurements from Grant (1997; available on the WPG website). Basically flow on the downstream portion of the wave is accelerating (Fr >1), while flow on the upstream portion is decelerating. The flow then oscillates between Fr > 1 and Fr < 1, maintaining overall flow at close to Fr ~ 1. Cross-sectionally averaged Froude Number tends to be slightly less, due to drag at the boundary. See paper for details.

The paper to which he refers is Grant, G.E. 1997. Critical flow constrains flow hydraulics in mobile-bed streams: a new hypothesis. Water Resources Research. 33: 349-358. PDF available here: http://www.fsl.orst.edu/wpg/pubs/criticalflow.pdf

For the best scientific coverage of the on-going Icelandic eruption, you absolutely can’t miss Erik Klemetti’s Eruptions blog. Erik is a volcanologist and has been doing an astounding job of keeping up with this (and all other volcanic activity). He also benefits from an active, engaged, and informed community of commenters to keep the rest of us up-to-the-minute on volcanic activity around the world.

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.

Sunday

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.