Author: Steve Stampfli, White Salmon, WA, USA, firstname.lastname@example.org
The first article in this series argued that American pikas living in hillside talus terrains are likely dependent upon steep, actively ventilated, blocky rock slopes that maintain moderated sub-surface temperatures via the chimney effect, at least in low-elevation regions like the Columbia River Gorge of Oregon and Washington. Since that article, however, I’ve been a little stumped by how that theory might ever be proven.
It initially seemed logical to use arrays of temperature loggers buried within Shellrock Mountain’s talus slopes to verify the location of active chimney effect talus processes, quantify slope temperature gradients, and pinpoint the location of hot and cold anomalies. Given enough study locations, loggers and effort, it might have been possible to correlate these locations and their thermal character to mapped pika occupations. Whether such a plan would have worked, however, is doubtful given the huge landscape scale. The examination of a new and likely better alternative is the subject of this article.
Shellrock Mountain sits about 10 miles west of Hood River, Oregon where the Columbia River has carved a deep gorge through the Cascade Range. The lower Columbia River Gorge is unique, given the fact it supports a very low-elevation population of American pika, a typically montane or alpine species that likely exhibits narrow temperature tolerances. Does the very unusual sea-level presence of pika in the Gorge indicate that this population has undergone some physiological adaptation to the region’s physical environment, or is it possible that the species is simply making use of some unrecognized aspect of its talus habitat?
The purpose of the first article in this science blog was to introduce the June 2017 discovery of an anomalous cold (possibly frozen) patch of ground on Shellrock Mountain’s northwest slope, and very near the most easterly population of low-elevation Gorge pikas. The article went on to hypothesize that based on the discovery of this cold zone (i.e., “Big Cold Vent”), a little known thermal mechanism known as the “chimney effect” could be responsible for anomalously cold conditions, and maintaining the temperatures of sub-surface talus pockets (i.e., refuge) utilized by pika within their required physiological range. The article concluded with a recommendation for further work at Shellrock to learn more about talus slope heat dynamics.
Because of ongoing highway work on I-84, plus safety concerns caused by last summer’s forest fire, all northern access to Shellrock Mountain has been closed by the Oregon Department of Transportation until 2019-20. The closure, therefore, eliminated any hope of installing arrays of continuous temperature loggers for the study of slope temperatures and quantifying pika thermal habitat. The situation forced an attempt to use remote temperature sensing, using LWIR (long wave infrared) images from the Washington shore for further investigation. In retrospect, the set-back resulted in a positive new direction for this project, since early LWIR results are promising.
The remainder of this article is a randomly organized photo-journal consisting of a series of LWIR images, preliminary interpretations, and discussions of future application in the study of talus slope processes and related plant and animal habitat. All of the images used in the article came directly from the thermal camera, with no post-processing of image quality.
Figure 1. Summer 2018 Shellrock Mountain LWIR mosaic overview.
Above is a mosaic of 10 individual LWIR images of the north slope of Shellrock, collected on a hot evening in early August 2018. The image covers a 0.56 mile reach of Oregon shoreline, and represents a good backdrop for the remainder of this article. This and following smaller-scale images were collected after dark during evenings of hot (90-100 degF) days, for maximizing summer hot/cold slope temperature gradients.
Note the high diversity of slope ground temperatures, and typical distributions (i.e., summer cold air venting zones being typically at the base of talus slopes, but not always). While temperature scales are shown on this and other images, use is only recommended for understanding relative temperature ranges. This is because target temperatures are attenuated by the atmosphere and atmospheric variables over distance. Understanding absolute temperatures or ranges might require “calibration” using in-situ slope temperature loggers and/or spot measurements. Depending on study goals, however, simple understanding of relative temperatures within scenes may be adequate. Other challenges in image analysis may arise from differences in target material emissivity, incidence angles, and reflection of heat coming from the sun and heated landscape. To minimize the reflection and maybe incidence angle challenges, all images were collected at night to eliminate heat interference from the sun, which is probably the biggest cause of reflected LWIR from dry vegetation and other reflective surfaces.
Big Cold Vent
The “Big Cold Vent” is the curious cold ground feature I located on the mountain’s northwest flank in June 2017. As hypothesized in the first article, this could be the location of a periglacial ice lens that formed within the base of the talus slope, as a result of chimney effect and Balch effect cooling. That conclusion is based on the fact that shallow ground temperatures did not rise above freezing until early August 2017. At the very least, it is the location of significant chimney effect cooling of the lower slope during summer.
The vent stands out like a beacon at the far right of Figure 2 below, and at the bottom of Figure 3. Interestingly, the coldest air seems to be venting out of the east side of the humped feature, where the slope was bared by an old landslide. The slide may date back to original Columbia River Highway or Interstate 84 construction. This could be where the ice core was intercepted and exposed by the slide, and/or where the coldest air continues to vent from the mountain’s talus veneer. Note too that warm slope conditions are visible to the left of the cold vent, resulting in a discontinuity in the mountain’s cold basal band. This discontinuity probably resulted from the same landslide, and subsequent removal of the material during clean-up of the slide. The now exposed post-slide hillside may lack the talus depth and mantle porosity required for chimney effect air circulation. This likely finding has an important real-world “management” implication, which is any dislocation of material from the base of talus slopes via talus rock mining, road maintenance, and road / edifice construction, can cause mass movements that modify or eliminate talus mantles, air and heat transfers, and dependent talus habitats. Another example is discussed in a later section of this article.
Figure 2. View of Shellrock Mountain and Big Cold Vent (right).
Figure 3 below shows a dominant aspect of Shellrock Mountain’s geomorphology (i.e., landscape form) that may help explain the strong cold talus effect and likely periglacial activity at the Big Cold Vent (see first article in this series). The mountain’s west talus slope has been over-ridden by successive landslides and other slope movements during the past thousands of years. As this deposition of mixed slope debris has occurred, the slow accumulation of well-sorted talus from the mountain’s west headwalls has continued. Depending on what process has been most dominant, talus might overlay the mixed slope debris, or mixed slope debris might overlay talus. Given the rate of landslide activity in the Gorge, however, it is likely that mixed slope debris deposition from the west has outpaced the slow and even generation of talus from Shellrock’s headwalls. Regardless, the photo shows that the two deposition processes have resulted in a descending truncation of the mountain cone’s talus slopes, trending from the south. The truncation likely assumes the form of a porous, subsurface trough of talus (likely overlain by slope debris) that collects, reservoirs, and transports the dense cold winter air across and down the mountain’s west skirt in summer. This might result in a “compound, 3-dimensional chimney effect”, where all the cold air concentrated in talus along the west side of the mountain is collected in the trough, and is ultimately transported down to the Big Cold Vent outlet just above the Columbia River. Such compounding would not occur if Shellrock Mountain rested on a flat plane, since there would be a multitude of cold air outlets instead of only one.
The effects of this hypothesized flow of cold surface and subsurface air are visible along the right side of Photo 3, although much of cold trough is invisible due to blockage by tall trees growing on the landslide slope. Confirmation of the compounding effect might be achieved in the future via the installation and monitoring of directional subsurface airflow meters and temperature loggers in the west slope talus and trough.
It is unknown whether pikas directly use the Big Cold Vent as habitat, as I have never observed them at the site. It is possible that direct occupation of this and similar vents would represent too cold and unvarying temperatures, even in summer. It is also likely that the north side of Shellrock Mountain lacks other important habitat features, such as big enough forefields for foraging and hay collection. These features are now greatly diminished due to ever growing human development activities (i.e., highway, railroad and recreational trail developments, and subsequent maintenance, recreational trail use, train and vehicle traffic, etc.).
Figure 3. View of Shellrock Mountain and hypothesized cold air “trough” descending to Big Cold Vent.
Slope Temperature Profiles
The following two images illustrate use of standard IR image analysis software (i3system, Inc.) for depicting custom point, line and area temperature contrasts within scenes. Some of the software’s basic functions, using the long-distance Washington-side images, were tried with positive results.
Figure 4 illustrates surface temperatures along the fall line, above and below the Big Cold Vent. Below the image is a graph showing pixel temperatures along the transect. Obvious is the cold vent temperature anomaly, and elevated temperatures of the interstate highway, railroad ballast, and shoreline. The limits of the cold vent anomaly are relatively confined from bottom to top, spanning maybe 150 feet along the fall line. Relative temperatures along the line where it transects the upper talus slope, and even Columbia River, seems consistent. This is despite the distance, high angles of incidence, and maybe surface reflection inconsistencies in both cases. The shape of the curve seems to be what would be expected for a thermally active talus slope undergoing summer chimney effect heat transfer. This remote and graphical means of charting slope temperatures may be a very suitable replacement for arrays of in-situ temperature loggers.
Figure 4. Fall line temperature transect.
Figure 5 shows a horizontal on-contour temperature profile of the same slope between “Twin Vents” (left) and “Big Cold Vent” (right), probably 40 vertical feet above highway level. The main reason for including this image is due to the camera and software’s ability to detect a small diameter temperature anomaly (13.4 degC) at the cold vent (the exact position is covered by the temperature scale). The cold anomaly is about 4 pixels wide, which at this distance would make it about 8 feet.
Figure 5. On-contour temperature transect.
The opportunities for using the technology demonstrated by figures 4 and 5 for both ecologic and geologic applications are many. First, LWIR imagery seems suitable for locating and roughly understanding thermally active slopes. In study designs, this might enable optimal placement of temperature loggers, siting of pika and other biological survey transects, etc. To enable this, it would probably be necessary to simultaneously incorporate both summer and winter images to map the location of both summer cold and winter warm vents. Second, IR might be suitable for use as the primary study method in geologic and ecologic studies, if imagery results were ground-truth calibrated using in-situ measurements.
Landslides and Other Talus Slope Features
Some of the big challenges in interpreting LWIR images involve segregating image effects caused by distance, target emissivity, angle of incidence, and target reflectance. When first beginning to analyze LWIR images of Shellrock, some of the data led me to suspect that mossy slopes might correlate with areas displaying cold talus conditions. It seemed probable that mosses would favor areas with cool, humid, uprising air currents during the heat of summer. While probably true, images such as Figure 6 cloud that conclusion. Here, it appears that many moss patches above the Big Cold Vent inhabit warm zones. There are at least two possible explanations for the discrepancy. First, mosses might be actively growing on both warm and cold slopes surfaces year-round. Second, it is possible that while mosses inhabit both areas, the patches seen on the upper warm slopes are dormant in summer, and only lower patches are actively growing then. Full understanding of surface temperatures will take more work to understand emissivity and reflectance occurring from active (growing), vs. dry (dormant) mossy surfaces.
It’s nevertheless clear that the images do a pretty good job of describing relative variations in landscape temperature. The infrared image in Figure 6 clearly shows very warm near-ground temperatures under the landslide slope (right) tree canopy in the early evening.
Figure 6. Heat blanketed below landslide slope tree canopy (right), and “hot moss” slope above Big Cold Vent.
Figure 7 below shows additional hillside processes that can likely be analyzed using LWIR. As noted earlier, a good percentage of the summer evening scene is dominated by warm tree canopies. Dry mosses may also be reflecting heat from the surrounding landscape, and like tree canopies, could be masking the temperature of talus surfaces.
Most interesting is the thermal character of the fall 2017 talus landslide. The bottom of the landslide shows as a granular and hot surface, likely due to the existence of large hot rocks with wide voids of separation. I believe that this type of rock sorting (largest clasts settling at the bottom of slopes, with smaller clasts settling upslope) is characteristic of landslides, and is the same as occurs during the artificial end–dumping of rock during construction of fill slopes. Assuming the effect seen in Figure 7 is typical, it would appear that neither landslides nor end-dumping are conducive to chimney effect ventilation in slopes, this being due to resulting top-to-bottom rock size gradation and overall poor rock sorting. Furthermore, landslides in particular might preclude chimney effect action on upper slopes if the entire layer of talus slides, and only poorly sorted, fines dominated, and ultimately non-porous hillside surfaces remain.
The above observations indicate that the formation of ventilated and functional talus habitats is probably the product of the gradual accumulation and slow movement of rock material originating from headwalls. If correct, this lends more support to the caution voiced earlier in this article concerning the need to protect the integrity of talus slopes during land management activities. The finding could also be important with respect to the creation of artificial talus slope habitats for pika and other organisms, if creation of artificial talus slope environments is contemplated via simple, end-dumping of rock.
Figure 7. Landslide and other talus features viewed using LWIR.
The final image in Figure 8 is included because it broadcasts the complexity of Shellrock Mountain’s thermal patterns, and potential usefulness in understanding how pikas and other animals and plants use such habitat features. But on a more basic and simple note, the image is simply a rare glimpse of the unexpected and unseen natural beauty of the Columbia River Gorge. Note the combination of likely chimney effect cooling evidenced by cold surfaces at the slope’s base, and possibly Balch effect pooling of cold air behind the I-84 retaining wall. The retaining wall is seen at the right, and just left of the large truck on I-84 with visibly hot wheels.
Though some of the slope surface is blocked by relatively warm tree canopies, it is obvious that summer thermal patterns in the talus landscape are varied and complex. Not all summer cool air venting occurs at the very bottom of such slopes, and warmer areas are intermingled with cooler zones. It is a mystery why some of the “cold air springs” visible on the image occur slightly upslope and above the usual band of cool air venting from the mountain’s base. Could there be areas of remnant ice just under the surface, confined “artesian” air conduits leading up from the cold talus cores, or simply layers of confining material directing the cold air outward prior to it reaching the bottom of the slope?
Figure 8. Complex summer cool venting (“cold air springs”), and Balch effect pooling on north side of Shellrock Mountain.
The ultimate goal of correlating pika seasonal activity at Shellrock Mountain with the mountain’s varied thermal features will be a challenge. It seems achievable, however, if a person could overlay pika census data atop geo-referenced LWIR imagery, and then search for trends. Such a task might be the perfect application for GIS analysis, and its ability to correlate population data to mapped features.
To get there, a method of tracking a population’s seasonal movement and activity would first be required. Second, accurate LWIR mapping and geo-referencing of summer cool zone and winter warm zone thermal features would allow the mapping of year-round subsurface habitat temperatures. Equating LWIR-derived surface temperatures with subsurface temperatures would be possible, given the fact that summer cold zone subsurface temperatures should be very close to LWIR-measured surface temperatures. Likewise, winter hot zone subsurface temperatures should be very close to LWIR-measured surfaces. This is because lower slope cold zone air venting (downward direction) is very rapid on the hottest days of summer, as is upper slope warm air venting (upward direction) during the coldest days of winter. Venting air speeds may be as high as 300 feet per day, according to modelling reported by Jonas Wicky and Christian Hauck in their 2017 “The Cryosphere” journal article.
Finally, the overlay of population tracking information on composite summer/winter thermal maps might allow understanding of how the animals are making use of favorable thermal habitats, in conjunction with mapped foraging areas, hay storage locations, breeding dens, etc. Final analysis may show, for example, that pika occupation and activities trend toward cold talus zones in summer, and warm talus zones in winter, as USFS researcher Connie Millar and I have both suggested possible. Millar has found that the “forefields” pikas use during foraging and hay collection are typically found at the base of cool talus slopes. Perhaps GIS analysis would also show that hay pile storage areas (used by pikas for supplemental winter food) are located upslope or adjacent to warm vent locations, and near areas the animals spend their winter months. Such areas are also often snow-free in active chimney effect environments, so would facilitate more surface feeding activity in winter.
Given the fact that such variable thermal diversity exist within such a limited geographic range, it would be very surprising if pikas (an animal with seemingly limited temperature and migration ranges) did not make extensive use of the compact thermal diversities offered in talus slopes.
I would like to sincerely thank Dr. Connie Millar of the USFS Pacific Southwest Research Station in Albany, CA for her interest, review, and comments on the draft article. Technical comments are likewise welcomed from anyone else on this version.