Department of Geography
University of Utah
Geomorphology Problem Set part of Cutting Edge:Geomorphology:Activities
This is an example of an exam//problem set I assigned to my Geomorphology class, which is a General Education offering at the U of Utah. The questions are rather generalized, but they can be answered to varying degrees, depending on how advanced the student is, or how much Earth Science they can synthesized.
Geo-Savvy Assessment part of Cutting Edge:Geomorphology:Activities
I use this "landscape interpretation" exercise to assess what students know coming into my classroom - so that I can pitch the lecture at the right level. I also use a similar structured assessment at the end of the course to evaluate individual learning outcomes.
Intro to Geomorphology: Mountains, Rivers, Deserts part of Cutting Edge:Course Design:Goals Database
This is a course that is listed BOTH as a General Education Physical Science Class, and as an upper level course for majors and graduate students.
Living on a slippery slope: Case studies of geologic hazards from the Wasatch Front, Utah part of Vignettes:Vignette Collection
Throughout their history, humans have fought the natural elements; we build shelters, roads, hospitals and malls wherever we can engineer "solutions" and strategies that permit us to thrive, even in harsh places. Using our brainpower, braun, and emerging technologies (like air conditioning), our builders, bulldozers and insurance policies allow us conquer the landscape... or do they? As population increases, "the built environment" encroaches places where Mother Nature reminds us of our vulnerabilities. This vignette examines some developed areas experiencing hazards in the Wasatch Mountain Front of Salt Lake City, Utah [Figure 1]. Here, houses are built on mountainous terrain that is affected by fires, floods and slope failures (Nicoll, 2010). What are slope hazards? Slope failures such as landslides, debris flows, and mudflows occur when materials (soils, rocks, etc) move downslope when the force of shear stress exceeds the shear strength of the material. Slope movements occur as stress (force per unit area) acts on a mass of rock or soil. Assessing whether the landscape is stable, or whether a failure might occur requires analysis of forces in relation to the slope morphology, geotechnical parameters, and the substrate material. After a landslide becomes active, the slope will continue to fail. Various geologists, geological engineers and technical scientists assess landscape stability and create hazard maps (Giraud and Shaw. 2007). What do unstable slopes look like? Even if you are a trained geologist with field experience, it may be difficult to recognize an unstable slope! Here, we examine a couple examples. In Figure 2, we look north (downslope) onto an ancient landslide deposit that moved off the Traverse Mountains and past the Steep Mountain Fault. The golf course was sited here due to the natural hummocky topography â hills and swales â that was created within the toe failure of a landslide. Recent construction work has extensively terraced this area. Along the fault scarp of Steep Mountain Fault, the developer has built a retaining wall. Something to think about: Given that there is both a fault and a landslide at this location, how can a potential homeowner determine how "safe" it is to live here? What are the potential benefits of this location? All of the homes depicted in Figure 3 are built within actively deforming deposits of the Little Valley Landslide (LVL). The ridge line is made of weak rocks -- rhyolite volcaniclastics of the Keetly Formation-- and there is a head scarp where the rocks have detached from the original mountain face. The initial rupture of the LVL is dated to ~15,000 years ago, because the landslide protruded into the ancient Lake Bonneville; stratigraphic relationships suggest that the LVL is younger than the "golf course" landslide deposits. Figure 3 was taken from the road, looking east from the graded road. To construct this road, engineers removed approximately half the original landslide material. The ridge in the foreground of the photo (left side of the image) is a pressure ridge where ancient landslide material piled up. Something to think about: Would you recommend living here? What are the main benefits, and the risks? What are the possible consequences of removing material from the toe or the edge of a landslide? The housing development in Figure 4 is situated upon a large landslide complex with multiple failure zones. The Landslide A has been deposited on top of another, older landslide deposit (outlined in orange) that was displaced by normal faults [Figure 1]. Much of the landslide material was removed to grade the road. Something to think about: The houses in this development are all built to code in that they are "set back" from known mapped geologic hazards. Is this adequate? How active are slope failures? Today, residents along the Wasatch Front occasionally observe debris flows. About 808 acres of the hillside at Corner Canyon burned in 2008, and areas downslope of the fire scar experienced flooding, mudslides and debris flows after intense rainfall in June 2009. Later, on 19 August 2010, mudflows affected many residents of Draper after another intense rainstorm. The National Oceanic and Atmospheric Administration (NOAA) reports that about an inch of rain fell in a 15-minute period, and this mobilized mud and debris (see website links below). The news reported water, mud flows and rock debris in people's houses and the streets near the mountain (see links to articles in Deseret News). More than 70 homes experienced damage and several roads were closed due to flooding and debris flows. Mud and water swept away trees, manhole covers and cars, broke through retaining walls and windows, and filled up the basements of more than 30 homes along the Wasatch Front. Something to think about: Are mudflows floods? Do you think that such homeowner damages caused by debris flows should be covered by "flood" insurance policies? In the case of these Draper homes, some of the affected properties are not built in the floodplain of a river (or canyon), and therefore technically not at flood risk. How should the flood risk of homes be evaluated? Why was this landscape developed? Since 2002, developers persuaded Draper City to annex and develop this land, using the argument that the property "tax base" would be lucrative. However, there have been many protests from geologists and engineers, who think the area presents significant risks. Since 2004, the developers have faced numerous technological challenges, slope failures, water rights issues, and safety violations, as well as the real estate crater following the market crash. Since 2008, several developers have gone bankrupt and many projects were aborted, with many homes presently bank-owned and saturating the market (Nicoll, 2010). One of the local controversies is the extent to which citizens should be advised of potential geologic hazards. For example, a hazards "information sign" developed by the Utah Geological Survey for posting at a park was opposed on the grounds that it would lower property values. Something to think about: Should information about potential hazards present in your backyard be publicized? Or should information about hazards be hidden from homeowners and prospective buyers? Are we making feasible development choices? Have we started to "over-populate" sub-ideal terrain? How can we design with Nature? Do property rights prevail over public safety?
Geomorphic Setting & Archaeology of the Cunene River, Namibia part of Vignettes:Vignette Collection
Introduction This vignette presents a virtual tour of the Cunene River, and a prehistoric archaeological site located on a fluvial terrace in northern Namibia. Today the Cunene River is an important transnational waterway and a critical reliable water source for the local nomadic Ovamba-Himba people who inhabit the Namib Desert. The Cunene is one of Namibia's largest perennial (regularly flowing) stream systems, and it flows through a landscape of stark contrasts. Its headwaters are located in the tropical rainforest of Africa, where its drainage morphology is dense and dendritic (Figure 1). Flowing downstream, the river incises through bedrock channels and flows through desert sands of the Cunene Sand Sea, as it flows towards its base-level along the foggy Skeleton Coast of the south Atlantic. Today, much of this region in southern Africa is a hyperarid desert, receiving less than 120 mm of rainfall per year. On the rare occasion of rainfall, this stark desert area can literally bloom into a grassland that attracts antelope and other game. Rock Controls the River Course Along its 344 km course, the Cunene River cuts through some of Namibia's oldest rocks. The main rocks that form the 300-400 meter high mountains shown in Figure 2 are garnet-bearing mica schists and gneisses; these metamorphic rock outcrops are part of a geological trend called the Kaoko Belt, a mountain terrane and volcanic complex that was active during the Proterozoic, more than 1500 million years ago. Within the area depicted in Figure 2 near the settlement called Cafema, the Cunene River is a mixed bedrock-alluvial system (see Tooth and McCarthy, 2004). The valley morphology appears to be strongly controlled by the local bedrock lithology and structure, and flood events are influenced by tropical rainfall affecting the headwater regions in Angola. The river course exploits geologic structures (including joints, foliations, and fracture orientations) in the bedrock, which is dominantly the Okapuka Formation, a metasedimentary unit. Foliation and joint-set lineation features in these "tough" rock outcrops help direct the river flow. Where the granitic gneisses and anorthosites are not easily eroded, the river encounters rapids and waterfalls. Prehistoric Terraces at Cafema After incising bedrock locally in the Cafema Mountains, the Cunene River valley widens dramatically for a few kilometers (see Figure 2). A 5 m high alluvial terrace along the left bank of the perennial river is mantled with a surface lag of cobbles and gravels (Figure 3), reflecting a time period when there was a greater fluvial discharge. Besides well-rounded gravels and cobbles, this terrace surface perserves a significant accumulation of Middle Stone Age artifacts. More than 30 stone tool or lithic artifacts were discovered in this open-air context (Nicoll, 2010). Among the finds were quartzite ﬂakes, cores, and characteristic stone tools with varying degrees of edge abrasion and varnish. Important Archaeological Finds Some of the artifacts found on the surface of the Cunene River terrace near Cafema have been fashioned in a characteristic style known as LevalloisâMousterian points. These artifacts are the ﬁrst of their kind found in this region of Africa. This archaeological assemblage is especially significant because the cultural history of this region during prehistory is poorly known. Finding these tools enable correlations with other sites across the continent for which ages are known, and suggest that these kinds of artifacts are at least 200,000 years old. The artifacts found in river terraces at Cafema provide some chronostratigraphic context for the fluvial development, and elevates the importance of studying river corridors in reconstructing hominin behaviours during the Middle Pleistocene -- the time frame marked by the ﬁrst appearance and the dispersal of the modern human species Homo sapiens "out of Africa." The Desert River becomes a Delta Through the Namib Desert to the west of the Cafema Mountains, the Cunene River flows through a vast hyperarid sand sea or erg (Figure 4), a wide plain with a variety of dune forms up to 400 m high. In the region south of the river, sands are piled up into many kinds of dunes, including longitudinal (long, linear dunes), barchans (crescent-shaped dunes) and star (star-shaped) dunes. The shape and orientation of the dunes are largely controlled by the direction and strength of the wind that blows the sand particles around. Where did all the sand come from? This is a good question â the sand may derived from erosion of rocks by the Cunene River over many tens of thousands of years. The river continues to flow westward to its local base-level of the South Atlantic Ocean, where it forms a delta, locally called the Foz do Cunene or "Cone of the Cunene" (Figure 5). Geoarchaeological Significance As a perennial river that traverses the hyper-arid Namib plain in its lower reaches, the Cunene River is a vital water resource in a dryland. The waterway is an oasis, providing resource and refugia during periods of seasonal or persistent drought. During antiquity, rivers and other permanent or ephemeral water bodies may have determined effective migration routes for hominin dispersal in southern Africa. As such, further geomorphic study of this river corridor has tremendous potential to inform what we know about the environments in which our human ancestors lived. In this case study of the Cunene River, geoarchaeological studies integrated with geomorphology help inform what we know about fluvial dynamics and human prehistory in this remote region of southern Africa.
A Case Study: Geomorphic Effects of the 2009 Big Pole Fire, Skull Valley, UT part of Vignettes:Vignette Collection
Introduction On August 6, 2009, a lightning strike caused the Big Pole Fire to break out in Skull Valley on private and Federal lands managed by the Bureau of Land Management, the US Forest Service, and the State of Utah. The ~43,923 acre fire affected the western Stansbury Mountains, located about 40 miles west of Salt Lake City, in Utah (Figure 1). This fire event provides a valuable opportunity to observe changes in the local semi-arid ecosystem and landscape. This vignette offers a virtual tour of the burn site and documents some geomorphic effects of the fire, including dust storms and erosion caused by sheetflow from two major thunderstorms in Late August and September 2009. Regional Geological Setting The Stansbury Mountains are located within the Basin and Range physiographic province, which is an extended terrain located west of the Rocky Mountains (Stokes, 1987). The Great Basin is characterized by a series of long, parallel, north and south trending ranges separated by broad valleys. Skull Valley is filled with unconsolidated alluvium, colluvium, and lakebed deposits derived from Lake Bonneville, the Pleistocene precursor of the modern Great Salt Lake. Geomorphology The Stansbury Mountains consist of Cambrian through Pennsylvanian quartzites, carbonates, and shales that were deformed during Mesozoic compression and Cenozoic extension. In general, the western side of the Stansbury Mountains is bound by a north-trending normal fault zone, and is a province with a moderately well-developed piedmont extending to the valley floors. Broad alluvial fans of cobbles and gravels coalesce off the mountain-front (Figure 2A). Elevations range from 4500 feet at the valley floor to over 10,000 feet on the highest peaks. The Big Pole Fire Burn Area In assessing a fire, analysts consider many variables, including the fuel available to burn, fire ignition, and other behavior such as the style of spread and the severity. Most of the area burned in the Big Pole Fire is located along a dry, west-facing 8-30% slope with poorly-developed soils comprised of very gravelly loam. Shadscale (Atriplex sp.) and sagebrush (Artemisia sp.) are major components of the steppe (Figure 2B), with antelope bitterbrush (Purshia tridentata), bluebunch wheatgrass (Pseudoroegneria spicata spicata), and bluegrass species (e.g., Sandberg Poa secunda) dominating the lower Skull Valley bottoms and piedmont; this region is currently not grazed. Upslope, the steppe includes Utah juniper (Juniperus osteosperma), mountain mahogany (Cercocarpus ledifolius), and serviceberry (Amelanchier utahensis or alnifolia) at mid-elevations, and becomes a mixed-conifer Douglas Fir (Pseudotsuga menziesii) and White Fir (Abies concolor) forest at the higher elevations and north-facing slopes. Ignition A lightning strike ignited the grasses in the timber understory, which is the prevailing fuel type in the region. In places where there was heavy timber pockets, single-tree torching occurred, and the fire took short uphill runs. Extreme fire behavior was experienced with rapid rates of spread and wind gusts > 50 mph. In many parts of the Skull Valley portion of the burn area, heavy fuel loads of sagebrush and dry grasses facilitated the complete consumption of available fuels; in patches where all vegetation was killed off, the landscape was left with no residual cover. The fire was deemed 100% contained by the USFS on August 16, 2009 @ 1700 hrs (red line, Figure 1). Fire frequency Typical fire return intervals in sagebrush-steppe ecosystems like the Stansbury Mountains are approximately 30-100 yrs, although this return interval has been shortened in many areas invaded by non-native grasses such as Bromus tectorum (cheatgrass); this species has invaded nearly 25 million acres of the Great Basin sagebrush steppe ecosystem (Bradford and Lauenroth, 2006). Cheatgrass quickly outcompetes native grasses -- it provides a fuel that is highly susceptible to fires, and it germinates and establishes early in the growing season before native perennial grasses can take hold (Mutch 1967; Bradford and Lauenroth 2006). Some studies demonstrate that cheatgrass dominance has reduced the mean fire return to less than 10 years. Enhanced fire frequency perpetuates cheatgrass expansion, quickly depletes the sagebrush seed bank, and converts native vegetation to an annual grassland dominated by highly combustible grasses (Whisenant 1990). Severity Fires in sagebrush-steppe communities are most often stand-replacing high severity fires. However, mixed severity fires are not uncommon. Burn severity is controlled by fuel continuity and density, as well as ambient weather conditions. During the Big Pole fire, both high severity and mixed severity burning occurred within the sagebrush-steppe and juniper-dominated fuels. Effects of a fire event Fire may be viewed as a disturbance event with cascading effects. Figure 3 shows a process-response diagram of the main effects after a fire disturbance. The main biotic effects of fire include replacement of invasive species and the forest stand. The geomorphic effects of fire include debris flows, landslides, and enhanced erosion by wind and water. Local water quality may also be adversely impacted. After a fire, surface runoff is often increased (Swanson, 1981). The combustion of vegetation and protective ﬂoor material (litter) results in the exposure of bare soil to overland ﬂow and raindrop impact (e.g., White and Wells, 1979; Wells, 1981), causing an increase in erosion. Fire-induced water repellent soil conditions and changes in hydraulics and infiltration further affect the local soil-water balance in burned areas. Following a fire, surface runoff and sediment yield may increase by a factor of 9-100 times the normal conditions (Giovannini and Lucchesi, 1991). Effects may be noticed within the watershed at the channel-to-hillslope scale. Observed Effects of the Big Pole Fire In the region affected by the Big Pole Fire, enhanced erosion was noted in the fire-affected region. Rills and gullies formed on the alluvial fan surface shortly after the fire (Figure 4). Enhanced sheetflow and erosional removal of the alluvium has created relief up to 3 feet (1 m) on an alluvial fan. Across the area burned by the Big Pole Fire, wind erosion was enhanced in places with exposures of bare soil via dust storms, saltation and deflation. A fire disturbance increases the erosivity of the land surface by impacting and killing-off the vegetation, decreasing surface roughness, and thereby increasing winds. Figure 5 depicts the degree of regional aeolian mobilization. A recent study of wind erosion following lightning-ignited wildfire in sagebrush steppe environments in Idaho documented that soil erosion increased following a fire, then diminished through the period of spring green-up to levels only slightly greater than in an unburned site (Sankey et al., 2009). In the sagebrush-steppe vegetation community, restoration efforts in the burned areas might include post-fire seeding in order to grow grasses to mitigate erosion. However, desert shrub steppe plants do not quickly re-establish, and it may take decades or centuries for a vegetative community to recover. Implications Since sagebrush steppe is one of the most threatened vegetation types in North America (Noss et al. 1995), it is critical to understand the abotic and biotic thresholds that influence its ecosystematics and sustainability in the face of disturbance such as fire. Future long-term studies might quantify the water runoff and sediment yield from burnt slopes. More fieldwork and vegetation mapping, in addition to several years of continual monitoring of the local meteorological conditions, runoff and erosional processes, will enhance our understanding of the interplay between fire disturbance and landscape processes.
Geomorphic Evolution of the Upper Basin of the Tigris River, Turkey part of Vignettes:Vignette Collection
Introduction The Tigris is one of Antiquity's famous rivers, as it flanks the fertile strip of land known as the Mesopotamian Plain, the heartland of the mighty biblical empires of Sumeria and Assyria (Figure 1). The Tigris River headwaters are at Lake Hazar in the Taurus Mountains of southeastern Turkey, in a highland region called the Eastern Anatolian Plateau (EAP). The EAP is part of the active Alpine â Zagros â Himalayan orogeny, a mountain belt that developed its topographic relief upon the closing of the Southern Neo-Tethyan Ocean, when the African and Arabian plates began colliding with Eurasia (Figure 2). Perhaps the most famous (or infamous) locale in this uplifted highland plateau is the ~5165 m (16946 ft) stratovolcano Mt Ararat, which is celebrated as the traditional resting place of Noah's Ark after the diluvian floodwaters departed. Why study Big Rivers in a collision zone? Study of large river systems like the Tigris provides insights about the interplay of lithospheric deformation and surface processes, as plates collide and mountains are built and eroded. The Tigris River has been geomorphically active over the past 13 million years, since the uplift of the EAP. Landscape features at aerial and ﬁeld scales show that the Tigris River valley morphology varies by reach, attesting to a complex evolution of the drainage system. First and foremost, the drainage morphology in the Upper Basin is linked to the uplift of the eastern Taurus Mountains, and deformation of the Arabian foreland system during continentâcontinent collision. The evolution of the Upper Tigris can be reconstructed as a function of vertical movement (e.g. base-level changes, tectonic uplift, doming, downwarp, and sagging), horizontal deformation (e.g. folding, faulting, compression, and extension), and volcanism. Weathering of the landscape has involved dissolution processes and karstic erosion of local carbonate and evaporite bedrock. This vignette summarizes the main influences on the geomorphic development of the Upper Tigris drainage system. To examine the primary controls on the drainage development, we will examine the geomorphic expression of the river along three main reaches, or sections of the river course, within the Upper Tigris Basin of Southeastern Turkey. Regional Setting and Surface Hydrology The modern climate in this part of the Tigris watershed is semi-arid with hot summers and cold winters; the average precipitation is about 580 mm, which mostly falls as snow. As such, the region is a cold-steppe desert with natural vegetation elements that include woody shrubs and occasional Mediterranean elements. Ice and snow melting from the EAP highlands are important water sources for the local drainages, and as the main source of drinking water for the large local population. The Aras (also known as Araxes) River drains eastwards to the Caspian Sea. The internally-drained or endorheic Lake Van Basin is rimmed by active volcanoes, including Mt. Ararat. The Upper Euphrates Basin is larger in size, with several long fluvial branches. The neighboring Upper Tigris Basin is smaller than the Euphrates Basin in area, and the development of its tributaries is strongly asymmetric. The Tigris River is separated from the Upper Euphrates Basin by a narrow topographic divide that is controlled by displacement along the East Anatolian Fault Zone, which is a strike-slip fault system comparable to the San Andreas Fault system in California (USA) (Figure 3). Headwater Reaches of the Tigris Emanating from its spring source at Lake Hazar, the Upper Tigris becomes a transverse river systemthat ﬂows across the strongly deformed metamorphic rocks that are part of the Bitlis â Zagros Suture Zone. Transverse drainages are discordant river patterns whose flow directions cut across geological structures such as faults, folds and the regional tectonic fabric in an area. Figure 4 shows how the course of the Tigris River in its headwater reaches cuts across the rugged structural grain evident in the metamorphic massifs making up the Eastern Taurus Mountains. A Transverse Stream Course After the Tigris cuts through the Taurus Mountains, the Tigris easily traverses a carbonate platform sequence (unit Tmls on Figure 4), upstream of Diyarbakir before it cuts across basaltic volcanic units (unit TQv on Figure 4). These Tertiary and Quaternary basalt flows are unconformable on the Tmls limestones and appear as the dark units north of Diyarbakir City. The basalts are strong units that buttress the river flow along its right (or south and westerly) bank. ...and an Antecedant Stream Course At the junction of the Arabian Plate south of the Suture Zone, the Tigris River may be viewed as an antecedent stream system that developed since the Miocene, after the close of the ancient seaway between the Afro-Arabian and Eurasian plates. An antecedent river has a drainage network pattern that was established in the geological past, and has remained preserved during regional uplift, because the rates of fluvial incision were higher than the rates of uplift. The antecedent river followed a course that parallels the developing orogen (dashed white lines on Figure 4). ...and then, a Karstic Stream Course East of Diyarbakir city, the river course shifts and trends east-west, as it erodes through fractured Miocene and Pliocene limestones, shales, and conglomerates that are thinly interbedded with salts. In this region, erosion of the bedrock (unit Tps) and valley widening is controlled by karst processes in bedrock made of evaporites and carbonate (Schumm et al., 1995) (Figure 5). Mapping in the area east of Bismil, sapping, piping, subsurface collapse features are apparent. The karstic processes are concentrated in folds paralleling the suture zone and the mountain orogen to the north (near the dashed white line in Figure 4). Sinkholes and groundwater sapping features have developed in the landscape during the past decade. Conclusions Continent-continent collision and resulting orogeny in this region of southeastern Turkey has exerted a strong control on the local geomorphology and drainage development. Tectonic uplift and defomation, in addition to rock lithology, are the prevailing controls on the Tigris River as it drains the highland area known as the EAP (Eastern Anatolian Plateau). Climate factors contribute to the erosion in the Upper Tigris Drainage Basin; karstic erosion is one of the processes that contributes to valley widening, particularly in areas where sedimentary rocks comprise the local bedrock.
Geomorphic Features in Little Cottonwood Canyon, UT part of Vignettes:Vignette Collection
Kathleen Nicoll University of Utah Location Continent: North America Country: United States of America State/Province: Utah City/Town: Salt Lake City and Sandy UTM coordinates and datum: 432313, 4494662 Northing ...