Fortress Mountain Research Articles

High‐Resolution Large‐Eddy Simulations of Flow in the Complex Terrain of the Canadian Rockies

AbstractImproving the calculation of land‐atmosphere fluxes of heat and water vapor in mountain terrain requires better resolution of thermally driven diurnal winds (i.e., valley, slope winds) due to differential heating by terrain and radiative fluxes. In this study, the Weather Research and Forecasting model is used to simulate flow in large‐eddy simulation (LES) mode over the complex terrain of the Fortress Mountain and Marmot Creek research basins, Kananaskis Valley, Canadian Rockies, Alberta in mid‐summer. The model was used to examine the temporal and spatial evolution of local winds and near‐surface boundary layer processes with variability in topography and elevation. Numerically resolving complex terrain wind flow effects require smaller grid cell size. However, the use of terrain‐following coordinates in most numerical weather prediction models results in large numerical errors when flow over steep terrain is simulated. These errors propagate through the domain and can result in numerical instability. To avoid this issue when simulating flow over steep terrain a local smoothing approach was used, where smoothing is applied only where slope exceeds some predetermined threshold. LES results from local smoothing were compared with a mesoscale model and LES with global smoothing. Simulations are evaluated using sounding data and meteorological stations. The differences in flow patterns and reversals in two mountain basins suggest that valley geometry and volume is relevant to the break up of inversion layers, removal of cold‐air pools, and strength of thermally driven winds.

Subalpine forest water use behaviour and evapotranspiration during two hydrologically contrasting growing seasons in the Canadian Rockies

AbstractHydrological processes in mountain headwater basins are changing as climate and vegetation change. Interactions between hydrological processes and subalpine forest ecological function are important to mountain water supplies due to their control on evapotranspiration (ET). Improved understanding of the sensitivity of these interactions to seasonal and interannual changes in snowmelt and summer rainfall is needed as these interactions can impact forest growth, succession, health, and susceptibility to wildfire. To better understand this sensitivity, this research examined ET for a sub‐alpine forest in the Canadian Rockies over two contrasting growing seasons and quantified the contribution of transpiration (T) from the younger tree population to overall stand ET. The younger population was focused on to permit examination of trees that have grown under the effect of recent climate change and will contribute to treeline migration, and subalpine forest densification and succession. Research sites were located at Fortress Mountain Research Basin, Kananaskis, Alberta, where the subalpine forest examined is composed of Abies lasiocarpa (Subalpine fir) and Picea engelmannii (Engelmann spruce). Seasonal changes in water availability from snowmelt, precipitation, soil moisture reserves yielded stark differences in T and ET between 2016 and 2017. ET was higher in the drier year (2017), which had late snowmelt and lower summer rainfall than in the wetter year (2016) that had lower snowmelt and a rainy summer, highlighting the importance of spring snowmelt recharge of soil moisture. However, stand T of the younger trees (73% of forest population) was greater (64 mm) in 2016 (275 mm summer rainfall) than 2017 (39 mm T, 147 mm summer rainfall), and appears to be sensitive to soil moisture decreases in fall, which are largely a function of summer period rainfall. Relationships between subalpine forest water use and different growing season and antecedent (snowmelt period) hydrological conditions clarify the interactions between forest water use and alpine hydrology, which can lead to better anticipation of the hydrological response of subalpine forest‐dominated basins to climate variability and change.

Meteorological observations collected during the Storms and Precipitation Across the continental Divide Experiment (SPADE), April–June 2019

Abstract. The continental divide along the spine of the Canadian Rockies in southwestern Canada is a critical headwater region for hydrological drainages to the Pacific, Arctic, and Atlantic oceans. Major flooding events are typically attributed to heavy precipitation on its eastern side due to upslope (easterly) flows. Precipitation can also occur on the western side of the divide when moisture originating from the Pacific Ocean encounters the west-facing slopes of the Canadian Rockies. Often, storms propagating across the divide result in significant precipitation on both sides. Meteorological data over this critical region are sparse, with few stations located at high elevations. Given the importance of all these types of events, the Storms and Precipitation Across the continental Divide Experiment (SPADE) was initiated to enhance our knowledge of the atmospheric processes leading to storms and precipitation on either side of the continental divide. This was accomplished by installing specialized meteorological instrumentation on both sides of the continental divide and carrying out manual observations during an intensive field campaign from 24 April–26 June 2019. On the eastern side, there were two field sites: (i) at Fortress Mountain Powerline (2076 m a.s.l.) and (ii) at Fortress Junction Service, located in a high-elevation valley (1580 m a.s.l.). On the western side, Nipika Mountain Resort, also located in a valley (1087 m a.s.l.), was chosen as a field site. Various meteorological instruments were deployed including two Doppler light detection and ranging instruments (lidars), three vertically pointing micro rain radars, and three optical disdrometers. The three main sites were nearly identically instrumented, and observers were on site at Fortress Mountain Powerline and Nipika Mountain Resort during precipitation events to take manual observations of precipitation type and microphotographs of solid particles. The objective of the field campaign was to gather high-temporal-frequency meteorological data and to compare the different conditions on either side of the divide to study the precipitation processes that can lead to catastrophic flooding in the region. Details on field sites, instrumentation used, and collection methods are discussed. Data from the study are publicly accessible from the Federated Research Data Repository at https://doi.org/10.20383/101.0221 (Thériault et al., 2020). This dataset will be used to study atmospheric conditions associated with precipitation events documented simultaneously on either side of a continental divide. This paper also provides a sample of the data gathered during a precipitation event.

Processes governing snow ablation in alpine terrain – detailed measurements from the Canadian Rockies

Abstract. The spatial distribution of snow water equivalent (SWE) and melt are important for estimating areal melt rates and snow-cover depletion (SCD) dynamics but are rarely measured in detail during the late ablation period. This study contributes results from high-resolution observations made using large numbers of sequential aerial photographs taken from an unmanned aerial vehicle on an alpine ridge in the Fortress Mountain Snow Laboratory in the Canadian Rocky Mountains from May to July in 2015. Using structure-from-motion and thresholding techniques, spatial maps of snow depth, snow cover and differences in snow depth (dHS) during ablation were generated in very high resolution as proxies for spatial SWE, spatial ablation rates and SCD. The results indicate that the initial distribution of snow depth was highly variable due to overwinter snow redistribution; thus, the subsequent distribution of dHS was also variable due to albedo, slope/aspect and other unaccountable differences. However, the initial distribution of snow depth was 5 times more variable than that of the subsequent dHS values, which varied by a factor of 2 between the north and south aspects. dHS patterns were somewhat spatially persistent over time but had an insubstantial impact on SCD curves, which were overwhelmingly governed by the initial distribution of snow depth. The reason for this is that only a weak spatial correlation developed between the initial snow depth and dHS. Previous research has shown that spatial correlations between SWE and ablation rates can strongly influence SCD curves. Reasons for the lack of a correlation in this study area were analysed and a generalisation to other regions was discussed. The following questions were posed: what is needed for a large spatial correlation between initial snow depth and dHS? When should snow depth and dHS be taken into account to correctly model SCD? The findings of this study suggest that hydrological and atmospheric models need to incorporate realistic distributions of SWE, melt energy and cold content; therefore, they must account for realistic correlations (i.e. not too large or too small) between SWE and melt in order to accurately model SCD.

An assessment of two automated snow water equivalent instruments during the WMO Solid Precipitation Intercomparison Experiment

Abstract. During the World Meteorological Organization (WMO) Solid Precipitation Intercomparison Experiment (SPICE), automated measurements of snow water equivalent (SWE) were made at the Sodankylä (Finland), Weissfluhjoch (Switzerland) and Caribou Creek (Canada) SPICE sites during the northern hemispheric winters of 2013/14 and 2014/15. Supplementary intercomparison measurements were made at Fortress Mountain (Kananaskis, Canada) during the 2013/14 winter. The objectives of this analysis are to compare automated SWE measurements with a reference, comment on their performance and, where possible, to make recommendations on how to best use the instruments and interpret their measurements. Sodankylä, Caribou Creek and Fortress Mountain hosted a Campbell Scientific CS725 passive gamma radiation SWE sensor. Sodankylä and Weissfluhjoch hosted a Sommer Messtechnik SSG1000 snow scale. The CS725 operating principle is based on measuring the attenuation of soil emitted gamma radiation by the snowpack and relating the attenuation to SWE. The SSG1000 measures the mass of the overlying snowpack directly by using a weighing platform and load cell. Manual SWE measurements were obtained at the intercomparison sites on a bi-weekly basis over the accumulation–ablation periods using bulk density samplers. These manual measurements are considered to be the reference for the intercomparison. Results from Sodankylä and Caribou Creek showed that the CS725 generally overestimates SWE as compared to manual measurements by roughly 30–35 % with correlations (r2) as high as 0.99 for Sodankylä and 0.90 for Caribou Creek. The RMSE varied from 30 to 43 mm water equivalent (mm w.e.) and from 18 to 25 mm w.e. at Sodankylä and Caribou Creek, which had respective SWE maximums of approximately 200 and 120 mm w.e. The correlation at Fortress Mountain was 0.94 (RMSE of 48 mm w.e. with a maximum SWE of approximately 650 mm w.e.) with no systematic overestimation. The SSG1000 snow scale, having a different measurement principle, agreed quite closely with the manual measurements at Sodankylä and Weissfluhjoch throughout the periods when data were available (r2 as high as 0.99 and RMSE from 8 to 24 mm w.e. at Sodankylä and from 56 to 59 mm w.e. at Weissfluhjoch, where maximum SWE was approximately 850 mm w.e.). When the SSG1000 was compared to the CS725 at Sodankylä, the agreement was linear until the start of ablation when the positive bias in the CS725 increases substantially relative to the SSG1000. Since both Caribou Creek and Sodankylä have sandy soil, water from the snowpack readily infiltrates into the soil during melt, even if the soil is frozen. However, the CS725 does not differentiate this water from the unmelted snow. This issue can be identified, at least during the late spring ablation period, with soil moisture and temperature observations like those measured at Caribou Creek. With a less permeable soil and surface runoff, the increase in the instrument bias during ablation is not as significant, as shown by the Fortress Mountain intercomparison.

Clinoform deposition across a boundary between orogenic front and foredeep – an example from the Lower Cretaceous in Arctic Alaska

AbstractThe Lower Cretaceous Fortress Mountain Formation occupies a spatial and temporal niche between syntectonic deposits at the Brooks Range orogenic front and post‐tectonic strata in the Colville foreland basin. The formation includes basin‐floor fan, marine‐slope and fan‐delta facies that define a clinoform depositional profile. Texture and composition of clasts in the formation suggest progressive burial of a tectonic wedge‐front that included older turbidites and mélange. These new interpretations, based entirely on outcrop study, suggest that the Fortress Mountain Formation spans the boundary between orogenic wedge and foredeep, with proximal strata onlapping the tectonic wedge‐front and distal strata downlapping the floor of the foreland basin. Our reconstruction suggests that clinoform amplitude reflects the structural relief generated by tectonic wedge development and load‐induced flexural subsidence of the foreland basin.

Migration pathways in the Central North Slope foreland basin, Alaska USA: solute and thermal constraints on fluid flow simulations

AbstractThe North Slope foreland basin, Alaska, USA is an east–west asymmetrical trough‐shaped basin adjacent to the Brooks Range fold‐thrust mountain belt. Lower Cretaceous age rocks make up much of the sediment fill, including flysch‐like marine turbidites and shales of the Torok and Fortress Mountain formations and marine and sandstones, shales and conglomerates of the overlying Nanushuk group. Lower Cretaceous age rocks were deposited on top of a Palaeozoic and Mesozoic age passive margin sequence. We have conducted numerical simulations of fluid flow driven by topographic recharge in the Central North Slope foreland basin. These simulations are constrained by salinity estimates from well logs, location of oil and gas fields, vitrinite reflectance and heat flow measurements. Our model results indicate that there are two south to north pathways for fluid migration. The primary pathway for fluid movement is downward through the Fortress Mountain formation, then upwards along the interface between the Fortress Mountain and Torok Formation and finally northward through the permeable Nanushuk group. A smaller mass of groundwater moves along sands below the Torok formation and into offshore sediments north of Alaska. Very little meteoric water enters the underlying Palaeozoic rocks in our simulations, which could explain the presence of deep saline pore waters. Our results also show that permafrost is a primary control on the pathway and rate of fluid flow by controlling the distribution of surface recharge and discharge. For example, areas of high heat flow and low saline waters along the arctic coast may represent upward groundwater discharge because of the absence of permafrost. As surface temperatures were warmer in the Miocene, the absence of permafrost would produce a more local fluid circulation pattern and less transfer of heat energy from south to north.

Against Barcelona?: Gaudí, the City, and Nature

March (Barcelona 1987), among other works. He is oho the editor of Catalonia, a Self-Portrait (Bloomington 1992). He currently serves as co-editor o/CatalAin Review. If you look North from the fortress mountain of Montjuic, across the rooftops of Barcelona, you will see the emerging mass of the church of the Holy Family, the Sagrada Familia. Once completed, if all goes according to plan, the mass will look like a mountain in the middle of the city. The mountainous appearance of the building was intentional from its conception and is central in the spatial thinking of Antoni Gaudi (1852-1926). As his biographer Gijs van Hensbergen reports, the architect joined the AssociaciA3 Catalana d'Excursions CientA-fiques in 1879, an organization devoted to the study of mountains (92). Gaudi's interest in mountains continued as he developed his ideas of nature (or Nature) as teacher. Notions of the mountain as a place of origin and purity abound in the literature contemporary with Gaudi's career (Sobrer). Barcelona sits at the foot of two guardian mountains: Montjuic and the peak of the Collserola range known as Tibidabo (a reference to Matthew 4.9, when the devil says to Christ: All these / will give you, if you will fall down and worship me). The Sagrada Familia, once completed, would triangulate the terrain. The end of the nineteenth century saw the emergence of plans for erecting some sort of vigilant church overlooking a crowded metropolis. A proposal was made in 1870 in Paris for the construction of the basilica of the SacrA© Coeur, or Sacred Heart, on a privileged position at the very top of Montmartre and fundraising began in 1873. The architect Paul Abadie designed the church in the Roman-Byzantine style. The first stone

Ozone and the clean troposphere: Ecological implications

In recent years numerous investigations have examined the relationships between chronic ozone (O 3) exposure and plant responses using statistical or empirical cause-effect models. One of the critically important decisions underlying these studies has been the choice of the control or reference O 3 exposure to which all other treatments are compared. The issue of the control or reference O 3 exposure is a complex one. Does a single ambient control or reference O 3 exposure exist? The approach taken in this paper is to examine the O 3 concentrations in the ‘clean troposphere.’ One must ask what a clean troposphere is and whether there are any geographic locations in the world today that are totally free of human influences. Data on photochemical oxidants from Fortress Mountain, Alberta, Canada, are examined. A comparison of these data with air quality data from other locations in North America is used to examine the design of vegetation response studies. The need for integrated research design, execution, and evaluation is stressed.

Fan-Delta Deposition in the Cretaceous (Albian) Fortress Mountain Formation, Central North Slope, Alaska: ABSTRACT

The Albian Fortress Mountain Formation at Atigun syncline is interpreted to be a proximal fan-delta depocenter. This interpretation is based on the absence of shale and marine indicators, the presence of indicative sedimentary features, and the discontinuous occurrence of this conglomerate in thick localized accumulations. The Fortress Mountain Formation crops out discontinuously across the Brooks Range foothills belt from west of the Kukpowruk River to the Sagavanirktok River. It is among the first sediments shed north into the Colville trough during early uplift of the Brooks Range orogen. In the central North Slope area, the Fortress Mountain Formation overlies deformed sediments of the pebble shale, Okpikruak Formation, and Konqakut Group. This study examines the Fortress Mountain Formation at Atigun syncline, near the eastern limit of its outcrop belt, where a 1,700-m section was measured and described during the 1989 field season. The Fortress Mountain Formation at Atigun syncline is composed of interbedded conglomerate (20%) and pebbly sandstone (80%). Significantly, shale is almost completely absent. The conglomerate is clast supported and consists dominantly of rounded and spherical chert pebbles and cobbles in a sandy matrix. Conglomerate beds are commonly ungraded and unimodal, with occasional crude imbrication. Most beds have planar basesmore » and tops, but some channeling does occur. While most beds are featureless, some sandstone beds are planar and trough crossbedded. Plant fragments are common on bedding surfaces.« less

Cretaceous Basin-to-Shelf Transition in Northern Alaska: Deposition of the Fortress Mountain Formation: ABSTRACT

The Fortress Mountain Formation (Albian) is a sequence of shale, sandstone, and conglomerate exposed as isolated synclinal outcrops in the southern foothills province of the Brooks Range. The formation overlies a variety of severely deformed older rocks, particularly the Okpikruak Formation of Neocomian age. The unit records a significant change in the depositional architecture of the North Slope Cretaceous and is closely tied to the evolution of the Brooks Range orogenic belt. Detailed stratigraphic and sedimentologic studies of the Fortress Mountain Formation within the type region and at easternmost exposures have demonstrated a systematic change in lithology and bedding style. The lower 40% of the Fortress Mountain is transitional with the Torok Formation and is composed of thick (up to 2,000-m) intervals of gray to black shale with thin, rhythmically interbedded, fine-grained sandstone beds. This succession is interrupted periodically by allochthonous blocks of conglomerate and conglomeratic sandstone. The sequences record a transition from basin plain to slope sedimentation. The middle 30-40% of the formation is composed of thick conglomerate and conglomeratic sandstone lenses that thin toward the north and are arranged in multiple upward-coarsening se uences and megasequences. End_Page 660------------------------------ Regional dispersal patterns indicate these beds accumulated within the midfan environment of a northward-prograding submarine fan complex. The upper 20-30% of the Fortress Mountain rests above a conspicuous angular discordance and is composed of upward-fining channel sequences of conglomerate, sandstone, and shale. This phase of deposition records progradation of fan-delta and fluvial environments. The regional depositional architecture of the Fortress Mountain records the buildup and sedimentologic evolution of the Cretaceous shelf, which ultimately allowed progradation of overlying deltaic and interdeltaic complexes of the Nanushuk Group and related strata. End_of_Article - Last_Page 661------------

Depositional History and Seismic Stratigraphy of Lower Cretaceous Rocks, National Petroleum Reserve, Alaska and Adjacent Areas: ABSTRACT

Knowledge of depositional history of Lower Cretaceous rocks in the National Petroleum Reserve in Alaska is necessary for predicting the occurrence of potential sandstone reservoirs. These rocks range in thickness from 7,000 + m along the Colville basin axis to about 1,200 m on the Barrow arch. Lower Neocomian strata on the north flank of the basin consist of southward-prograding marine shelf and slope deposits of shale and minor sandstone units. Uplift, erosion, and subsequent transgression on the northernmost flank of the basin resulted in deposition of the pebble shale unit in late Neocomian time and termination of the northern provenance. Following this, the basin was downwarped, and little deposition occurred on the north flank until distal, deep-water deposits of the Torok Formation onlapped and downlapped the south-dipping flank of the basin in middle or late Albian time. On the south flank of the basin, southern-source turbidites of the Okpikruak Formation (early Neocomian) accumulated in a subsiding foredeep and were subsequently thrust northward in late Neocomian or Aptian time. The Fortress Mountain Formation (early Albian), which consists of as much as 3,000 m of mainly deep-water deposits, unconformably overlies the Okpikruak and older rocks on the southernmost flank of the basin. Filling of the Colville basin occurred in middle to late Albian time as thick prodeltaic and deltaic deposits of the Torok Formation and Nanushuk Group, respectively, prograded across the basin from the south on the south side of the basin, but prograded principally from the west-southwest over most of the basin. End_of_Article - Last_Page 670------------

Depositional History and Seismic Stratigraphy of Lower Cretaceous Rocks, National Petroleum Reserve, Alaska and Adjacent Areas: ABSTRACT

Knowledge of depositional history of Lower Cretaceous rocks in the National Petroleum Reserve in Alaska is necessary for predicting the occurrence of potential sandstone reservoirs. These rocks range in thickness from 7,000 + m along the Colville basin axis to about 1,200 m on the Barrow arch. Lower Neocomian strata on the north flank of the basin consist of southward-prograding marine shelf and slope deposits of shale and minor sandstone units. Uplift, erosion, and subsequent transgression on the northernmost flank of the basin resulted in deposition of the pebble shale unit in late Neocomian time and termination of the northern provenance. Following this, the basin was downwarped, and little deposition occurred on the north flank until distal, deep-water deposits of the Torok Formation onlapped and downlapped the south-dipping flank of the basin in middle or late Albian time. On the south flank of the basin, southern-source turbidites of the Okpikruak Formation (early Neocomian) accumulated in a subsiding foredeep and were subsequently thrust northward in late Neocomian or Aptian time. The Fortress Mountain Formation (early Albian), which consists of as much as 3,000 m of mainly deep-water deposits, unconformably overlies the Okpikruak and older rocks on the southernmost flank of the basin. Filling of the Colville basin occurred in middle to late Albian time as thick prodeltaic and deltaic deposits of the Torok Formation and Nanushuk Group, respectively, prograded across the basin from the south on the south side of the basin, but prograded principally from the west-southwest over most of the basin. End_of_Article - Last_Page 670------------

Pennsylvanian and Permian Biostratigraphy, Micropaleontology, Petrography and Diagenesis, Kananaskis Valley, Alberta

ABSTRACT A roadcut on the improved Kananaskis Forestry Trunk Road, near Fortress Mountain Junction, exposes the Pennsylvanian Spray Lakes Group (McGugan and Rapson, 1963) including the Lower Pennsylvanian Tunnel Mountain Formation (restricted, McGugan and Rapson, 1961), overlain disconformably by the Lower Middle Pennsylvanian (Lower Atokan, Bashkirian to Lower Moscovian) Kananaskis Formation (McGugan and Rapson, 1961) with Profusulinella cf. fittsi (Thompson), in turn disconformably overlain by the Lower Permian Johnston Canyon Formation, Ishbel Group (McGugan and Rapson, 1963). Considerable relief can be demonstrated on the disconformities involved. Reliable correlations can be made south to the Elk Valley and west and north to the type section of the Kananaskis Formation on Mount Chester and the well-known succession on Tunnel Mountain, Banff. East of the Kananaskis Valley on the Front Range, thin but laterally persistent Pennsylvanian and Permian feather edge condensates are developed toward the easterly shoreline, and rocks of these ages are absent in the Foothills subsurface farther east. The Kananaskis Formation is correlative with carbonate erosional remnants named the Hanington Formation (Bamber and Macqueen, 1979) with Profusulinella in northeastern British Columbia. Rocks of similar age, with Profusulinella, have been reported from Utah, Oklahoma, Texas, the Russian Platform and China.

Plant megafossil sequences, north slope cretaceous

Abstract An Albian to Maestrichtian plant megafossil sequence in northern Alaska is documented by assemblages from 250 localities distributed through about 23,000 feet of section in seven study areas across 350 miles of the North Slope. The megafossil records are referred to formal rock units that range upward from Albian Torok—Fortress Mountain levels through the Albian—Cenomanian Nanushuk Group and the Turonian—Maestrichtian Colville Group. More than 380 plant species are recognized at present. Eight biostratigraphic zones totaling 21 subzones have been established: IA (oldest) and IB—fern‐ginkgophyte‐cycadophy te ; II—fern‐ginkgophy te‐cycadophy te‐coni‐fer; III—fern‐ginkgophyte‐cycadophyte‐conifer‐dicot; IV—conifer‐dicot; V to VII—predominantly dicots with conifers subdominant. Floral data from numerous levels suggest rapidly fluctuating conditions over the northern Alaska region during Cretaceous time. Floras and climates may have changed as rapidly in the later part of the Mesozoic era as they did i...