Hi! Chris has graciously been cajoled into formally sharing this blogging space with him. I am thrilled and honored to become a semi-irregular co-blogger at Highly Allochthonous. Hopefully, between Chris and I we can manage to provide interesting and witty content on a more regular basis. I’ll leave the witty part mostly to him, though.
I’ve been sporadically guest blogging here for a year or so, but I never properly introduced myself, so now is my chance. I’m an assistant professor at UNC Charlotte, with origins in the Driftless Area of southeastern Minnesota and the Cascades of Oregon. I have a hard time defining what exactly I do, but it tends to blend hydrology with geomorphology, geology, and/or climate. Right now I’m in the midst of a flurry of grant applications, so my take on the fascinating reports of groundwater withdrawals in India will have to wait, but if you have lingering curiosity for how one blends water, rock, and air, you can go below the fold for a description of the field trip I’m helping lead at the upcoming Geological Society of America meeting and a couple of abstracts from the same meeting.
Here’s the pre-meeting field trip I’ll be helping out with. Parts of it are based on my PhD research. The scenery will be gorgeous, the topic scintillating, and the company superb. Will I see you there?
Fire and Water: Volcanology, Geomorphology, and Hydrogeology of the Central Cascades and Adjacent Areas, Oregon
Thurs.-Sat., 15-17 Oct.
This trip will explore the interactions among the geologic evolution, hydrology, and fluvial geomorphology of the central Cascade Range in Oregon. This region offers an unparalleled opportunity to examine over 30 million years of landscape development along a young volcanic arc amidst spectacular natural scenery. Key topics to be examined include the geologic control of hydrologic regimes on both the wet and dry sides of the Cascade crest, groundwater dynamics and interaction between surface and groundwater in volcanic arcs, changing evolution of volcanic styles and products from the Miocene to the Holocene, and interactions between rivers and lava flows. We will also consider the history of and controls on channel incision. Along the way, we will trace the Willamette River back to source springs high in the young volcanic rocks of the Cascades, cross the divide, and then follow the Deschutes River from its source downstream, where its deep canyon has cut through the entire Neogene section, capturing both regional groundwater flow and volcanic flows from the Cascade arc.
The field trip is perfectly paired with a Pardee keynote symposium (T8) on “The Evolution of Basaltic Landscapes: Time and the River and Lava Flowing” and a technical session (T27) on “Hydrologic Characterization and Simulation of Neogene Volcanic Terranes” In the latter session, I’m an invited speaker:
On a template set by basalt flows, hydrology and erosional topography coevolve in the Oregon Cascade Range
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.
Closer to my present home and work, I’m helping convene session T31: “Stream-Groundwater Interaction: New Understanding, Innovations, and Applications at Bedform, Reach, and River Network Scales.” In that session, I’ll be presenting a poster with co-authors from the North Carolina Division of Water Quality.
Groundwater contributions to headwater streams on fractured rock in the North Carolina Piedmont and Blue Ridge
Anne Jefferson (UNCC), Joju Abraham (DWQ), Ted Campbell (DWQ), and Cameron Moore (UNCC)
Baseflow is generally assumed to homogenously accrete into headwater channels through flow from soil and porous bedrock, but on crystalline rocks there may be discrete up-welling and down-welling zones associated with fractures. Despite the prevalence of fractured crystalline rocks in the Appalachians and Piedmont of the eastern United States, little work has been done to document and understand groundwater-stream interactions in fractured rock environments.
At three sites in the North Carolina Piedmont and Blue Ridge provinces, groundwater and first-order streams were monitored for temporal and longitudinal temperature and water quality patterns. Stream temperatures at all sites have strong diurnal and seasonal fluctuations, while streambed sediments show smaller diurnal variability. Near-stream piezometers and wells show no diurnal temperature fluctuations, and seasonal fluctuations lag air temperature changes by 1-7 months or are absent. These lags generally increase with depth. In response to rainfall events, a shallow well in a discharge zone at one site (Bent Creek) showed temperature perturbations within 18-20 hours, suggesting upwelling from deeper flow zones. At another site (Allison Woods), rainfall perturbed groundwater temperatures in piezometers screened 1-2.4 m below land surface, but not in wells screened 2.1-7 m below land surface, suggesting groundwater recharge. There is a general trend towards downstream heating in the summer, but several temperature probes deviate from this trend, and synoptic surveys show that some areas with depressed temperatures have elevated specific conductance. These results suggest that there are distinct groundwater upwelling areas within the streambed. At one site (Deep Creek), seasonal variation in stream water isotopes suggest that baseflow is sourced in water <5 years old. Some streams also have ephemeral reaches that correspond with debris jams and sediment wedges, where all baseflow infiltrates into the stream bed. In other reaches, the streams flow on bedrock with fine alluvium banks and hyporheic exchange may be quite limited. Ongoing work aims to understand the relative importance of hyporheic exchange versus fracture systems in setting the patterns of groundwater-surface water interactions in Piedmont and Blue Ridge headwater streams.
I’ll also have a graduate student presenting a fluvial geomorphology poster and I’m helping Kim Hannula out with her survey of women geoscientist bloggers, so it will be a busy and fun meeting for me. See, I’m already setting the stage for pulling a disappearing act in October.
Thanks again to Chris for letting me intrude on his space, and I look forward to interacting with the good readers of Highly Allochthonous in the months to come.