GEOL 553 Lab 3: Glacial Landform Mapping
Name_______________________________________ Date: ____________________
Summary
In this lab, students learn about glacial landforms as preserved along the Wasatch front in
northern Utah. The Wasatch fault, the easternmost extent of the North America/Pacific plate
boundary, extends along the base of the mountains on the east side of Salt Lake City. The
Wasatch Range has been glaciated, most recently during the Last Glacial Maximum (LGM).
Glacial, Glaciofluvial, and Glaciolacustrine landforms can be identified at the base of the
Wasatch Range, near Sandy and Draper, Utah (a part of SLC). Students will map the landforms
using stereo aerial imagery, digitize their interpretations using a GIS, create a map, and write a
report with the map as one of the figures.
Goals
Students will learn the following:
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To become familiar with glacial, fluvioglacial, and lake shoreline landforms
To become familiar with mapping these landforms using stereo air photos
To learn how to map these landforms in a GIS software application
Background
Lake Bonneville began rising from a low level about 30 ka and rose slowly (transgressive phase),
with several fluctuations and pauses, to the Bonneville shoreline (1537-1585 m [5160-5200
feet] above sea level) about 16ka. After 1000-2000 years at that level, the lake dropped about
110 m (360 ft.) to an altitude of about 1465 m (4800 ft. - Provo shoreline) as a consequence of
catastrophic down cutting of its outlet in southeastern Idaho. The resulting Bonneville Flood
deposited debris northward into southern Idaho. In the SLC area, this rapid decline in lake level
was accompanied and followed by rapid erosion of existing lacustrine transgressive-phase sand
and gravel and other glacial-outwash and alluvial-fan deposits; much of this debris was
redeposited as deltas at the Provo shoreline near the mouths of major canyons. Between 14
and 13 ka, the lake level again dropped quickly, this time in response to changing climatic
conditions, to further down cutting of its outlet, and to isostatic rebound of shoreline areas.
Lake Bonneville reached a level near that of modern Great Salt Lake (1280m; 4250 ft.) about 11
ka and rose briefly to the Gilbert shoreline (1295 m; 4250 ft.) 10-10.5 ka. Since then, the lake
level has remained within 10 m of the level of present Great Salt Lake.
Glaciers in Little Cottonwood and Bells Canyons advanced beyond the Wasatch Range and into
the eastern Salt Lake Valley 26-18 ka, while Lake Bonneville stood at a low to intermediate level
during the transgressive phase that eventually saw the lake rise to the Bonneville shoreline. Till
deposited by these glaciers forms large end moraines extend nearly 1 km into the valley beyond
the mountain front. This is one of only two localities in the U.S. where Pleistocene glaciers
descended below shorelines of pluvial lakes. G.K. Gilbert in 1890 recognized that "the relations
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GEOL 553 Lab 3: Glacial Landform Mapping
of these moraines to the shores of the lakes and the associated deposits indicate that the
maximum stage of the lakes coincided closely with the epoch of maximum glaciation."
Meltwater from these glaciers and from glaciers in Big Cottonwood Canyon deposited gravelly
outwash fans along the range front and deltaic deposits in Lake Bonneville. Other streams,
emanating from valleys in the Wasatch Range whose headwaters were at altitudes too low to
support more than small glaciers, also deposited gravelly fans and deltas graded to the lake.
The rising lake culminated at the Bonneville shoreline about 16 ka, several thousand years after
the glaciers in Little Cottonwood and Bells Canyons had retreated some distance up-valley from
their end moraines. The outwash and alluvial-fan deposits along the mountain front also were
inundated by the rising lake and, except for small areas near the canyon mouths that stood
above the level of the lake, are covered by a veneer of lake sediment. The combined outwashfan-and-delta complexes form the highest surfaces along the range front.
Note the time lag between retreat of the glaciers up-valley and the maximum lake level. The
rise and fall of Lake Bonneville is not a simple matter of glacial ice melting and filling the lake. In
fact, the volume of water in the glaciers is not enough to account for the volume of water in the
lake. Climate is a large factor. Interglacial periods are warm, so there is more evaporation, but
also more precipitation. Glacial periods are the opposite.
Much of the gravel mined along the range front represents classic Gilbert-type deltas built at
and below the Provo shoreline near the mouths of major canyons in the initial phases of the
regressive phase. Straths cut at this time can be seen on the south side of Big Cottonwood
Creek. The long, steep foresets of these deltas were at one time visible in a few of the pits. The
great bulk of deposits at the Provo shoreline is due to the large volume of sediments in the
high-shore zone at the mouths of major streams that were available for erosion and redeposition following the rapid lake-level change.
As the level of Lake Bonneville receded from the Provo shoreline during the regressive phase,
alluvial-fan deposits and debris-flow deposits were emplaced at canyon mouths along the
mountain front. Rates of alluvial-fan deposition appear to have declined later in the Holocene,
because deposits of late Holocene age are restricted to small deposits covering parts of the
surfaces of much larger alluvial fans.
Pre-Bonneville-lake-cycle deposits are limited to small remnants of alluvial-fan and glacial-drift
deposits. Till of the Dry Creek advance is exposed at the mouths of Little Cottonwood and Bells
Canyons. Till is weathered to a degree that suggests an age of about 150 ka, correlating with
Bull Lake-aged moraines in the Rocky Mountains. Outwash of probably the same age is exposed
in gravel pits near the mouth of Big Cottonwood Canyon and along Dry Creek downstream from
Bells Canyon.
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GEOL 553 Lab 3: Glacial Landform Mapping
Figure 1. Landforms and deposits associated with continental glaciers.
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GEOL 553 Lab 3: Glacial Landform Mapping
Figure 2. Landforms and deposits associated with alpine glaciers.
Depositional Landforms
As ice melts it leaves behind the sediment carried within it. This sediment can be piled around
the edges or beneath a glacier as it melts, or the sediment can be directly deposited beneath
active, moving ice. Subsequent advances of a glacier can rework and destroy landforms created
by previous advances. Glacial depositional features include:
• Moraines. The debris deposited directly from the glacial ice is called moraine. Terminal
moraines are deposited at the leading edge of a glacier, lateral moraines are deposited at the
sides of a glacier, and ground moraine is deposited beneath the glacial ice. Medial moraines
may form where two glaciers flow together, sandwiching their lateral moraines within the
new, combined glacier.
• Drumlins. Streamlined hills formed in sediment or bedrock that form beneath glaciers.
Drumlins are elongated in the direction of ice motion with steep faces pointed uphill.
• Outwash plains. Much of the finer sediment may be washed away from a glacier by
meltwater. The meltwater deposits this sediment over a broad outwash plain.
• Kettles. Blocks of ice may be isolated from the main glacier as it recedes and become
surrounded and covered with moraine or outwash sediment. As the block melts, the
overlying sediments collapse, leaving a depression called a kettle.
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GEOL 553 Lab 3: Glacial Landform Mapping
• Eskers. Streams flowing on, within, or below glaciers can deposit ribbons of channel
sediment just like those flowing in channels within bedrock. When the ice melts, these
ribbons of sediment are left behind as ridges called eskers.
Glacial Sediments
Sedimentary deposits left by glaciers are highly variable in terms of their sorting and grain size.
Common deposits found in glacial and near-glacial environments include:
• Till. This is sediment deposited directly from the ice. Moraines consist of till. Till is typically
very poorly sorted and has angular grains. There is typically no bedding in tills. Often,
continental tills have a bimodal grain size, with a fine-grained matrix and larger clasts. (The
non-genetic term for bimodal sediment is diamict.)
• Stratified drift. This is a catch-all term for glacial sediments that have been somewhat
reworked by water. This kind of deposit is common along ice margins where sediment is
released from the ice and moved by meltwater. It is often poorly sorted with pockets or
lenses of well-sorted sand.
• Glaciofluvial deposits (outwash). Meltwater streams can re-work sediment deposited by the
glacier. These streams are often steep, have very high sediment loads, and are braided
instead of meandering. Outwash deposits are typically better sorted than tills, as the finest
grains have been washed away, leaving cross-bedded sub-rounded to well- rounded sand,
gravel, and cobble-sized clasts. Outwash develops in front of advancing and retreating
glaciers. The size of the sediment can be a function of the proximity of the glacier, with larger
clasts remaining closer to the glacier.
• Glaciolacustrine deposits. Glaciers can block streams and create pro-glacial lakes. Sediment
carried into these lakes settles on the bottom. Typically, the coarse-grained sediment settles
near the edges, where streams enter the lake. Fine-grained sediment (silt and clay) can be
carried out to the middle of the lake, where it can form very thin layers called laminations.
Sometimes, sediment-rich icebergs can carry larger clasts out to the middle of a lake, melt,
and drop them into the finer-grained sediment. These large clasts found within finer-grained
lake sediments are called dropstones.
Glacial Stratigraphy
The history of glacial advances and retreats are unraveled through their deposits. Because
glacial ice advances and retreats, the type of sediment deposited in a glacial environment is
highly dependent upon where the ice is through time. For example, an outwash plain in front of
a glacier may get overridden by that glacier, resulting in a layer of outwash capped by a layer of
till. Similarly, till left by a retreating glacier may become covered by outwash as the ice retreats.
However, because glaciers and the associated streams are very erosive and deposition is often
irregular, deposits can have irregular (non-horizontal) contacts and entire layers may be
missing.
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GEOL 553 Lab 3: Glacial Landform Mapping
Part I. Mapping Glacial/ Glaciofluvial /Glaciolacustrine Landforms
Use stereo air photos to map glacial, Glaciofluvial, and Glaciolacustrine landforms at the mouth
of Little Cottonwood Canyon. Glaciofluvial landforms include landforms that one would
typically map as fluvial landforms. Glaciolacustrine landforms include landforms that one would
typically map as lacustrine landforms. The only difference is that these landforms are related to
processes related to glaciation and pluvial forcing factors. Trace the different landforms and
label them onto your tracing paper. You will use this map as a guide when you digitize the
features in the GIS system.
Aerial photographs are an important supplement to topographic maps. They provide detailed
views of the Earth’s surface and, when viewed stereoscopically (in three dimensions), show
subtle topographic features, vegetation patterns, and textural differences, which cannot be
expressed simply by contour lines.
Vertical aerial photographs are usually taken sequentially along a predetermined flight line
(Figure 3A). Photographs are taken frequently, and each photograph includes a portion of the
land area shown on the previous picture. Flight lines try to attain approximately 60%
photographic overlap. When a portion of the overlap area is viewed through a stereoscope,
each eye sees exactly the same area, but at different angles and on different photographs
(Figure 3B). The view through the stereoscope approximates that of an observer suspended
over the original landscape. As a result, the two photographs merge into one, thereby creating
a three-dimensional effect.
Figure 3. Diagrams illustrating vertical aerial photography and stereoscopic viewing. (A) The
photograph taken over location 1 covers the ground area indicated. The photograph taken over
location 2 includes about 60% overlap with the area covered by photograph 1. (B) A
stereoscope is used to restore original angular relationships and obtain a three-dimensional
view of area of overlap.
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GEOL 553 Lab 3: Glacial Landform Mapping
Part II. Digitizing Landforms
Use ArcMAP to digitize the landforms that have been mapped using the stereo air photos. Add
spatial data including topography, aerial imagery, and topographic imagery to help collocate
features found on the air photos with those in the digital GIS space. We may use polyline data
sets and/or polygon data sets.
A map is a two-dimensional representation of a portion of the Earth’s surface. Most maps used
today are planimetric, which convey data on a two-dimensional surface. Planimetric maps may
provide information about transportation routes, geographic location, nominal data, vegetation
patterns or other forms of data requiring spatial representation.
LIDAR (a portmanteau of “light” and “radar”) mapping, also described as Airborne Laser Swath
Mapping (ALSM), utilizes an airborne scanning laser rangefinder to produce detailed
topographic surveys. This relatively new mapping technique produces more comprehensive and
precise topographic data than traditional methods. One of its unique properties is that airborne
laser altimeter data can be used to accurately measure topography even when vegetation
growth is extensive, such as forested terrains.
Accurate topographic data is acquired by precisely timing the round-trip travel time of a pulse
of laser light from the airplane to ground surface and back. The travel-time is converted to
distance from the ground to the plane knowing that the laser pulse travels at the speed of light.
Laser transmitters fire thousands of pulses per second, which provides very detailed distance
data of the surface below. The airplane’s location at the time that a given set of laser pulses is
emitted is accurately determined using a global positioning system (GPS). The distance
measurements and GPS data are then converted to detailed map coordinates and elevation
data coincident with individual laser pulses.
Large surface areas are mapped by flying many parallel flight lines ensuring that there is
adequate overlap for complete coverage. Newer laser technology can measure multiple
reflected returns so that vegetation cover can be identified and “removed” from the mapped
surface by comparing the multiple returns with the “last return” (inferred to be from the actual
ground surface). High resolution LIDAR imagery has many applications important to the geoand environmental sciences, as well as urban and rural planning.
For more detailed and complete information regarding LIDAR imagery, techniques and
applications refer to the Puget Sound LIDAR Consortium’s web site at:
http://pugetsoundlidar.ess.washington.edu
Prepare a map using the digitized linework and any combination of other background data that
will help locate your line work. On the GIS laboratory computers are loaded the following data
sets: Digital Elevation Model (DEM) and shaded relief rasters at 10 m resolution, National Aerial
Imagery Program (NAIP) real color imagery at 1 m resolution, USGS Topographic Map Imagery
(DRG, Digital Raster Graphic), and LIDAR DEM and shaded relief rasters at 2 m resolution.
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GEOL 553 Lab 3: Glacial Landform Mapping
Create shapefiles that can be edited to delineate the different landforms. Create a map with
these landforms symbolized for usability, with a legend, a scale bar, a north arrow, and any
important notation. Use the different raster data sets at varying levels of transparency to
enhance your map. Feel free to make several maps with different combinations of raster base
data.
Part III. Questions and Report
Prepare a report with the map from part II as a figure. The report will include the standard
sections (introduction, methods, results, discussion, and conclusion). The report will include
answers to the following questions as part of the discussion and conclusions.
Questions:
What types of landforms were you able to map? Define the landforms and describe how the
landforms were created.
Is there evidence for different lake levels? If so, what is this evidence and where is it located on
your map? Is it Glaciofluvial, Glaciolacustrine, both, or neither?
Is there evidence for fluvial landforms that may be related to the evidence for lakes? If so, what
is this evidence and where is it located on your map?
Is there evidence for receding glaciers? If so, what is this evidence and where is it located on
your map? Is there evidence for multiple glaciations? If so, how did you come to this
conclusion? Describe the evidence you used to form this conclusion.
GIS data sources:
LiDAR data (2m) http://gis.utah.gov/data/elevation-terrain-data/2-meter-lidar/
Basics about LiDAR: https://en.wikipedia.org/wiki/Lidar
More about LiDAR: http://www.opentopography.org/index.php/resources/education
DEM data (10 m) http://gis.utah.gov/data/elevation-terrain-data/10-30-90-meter-elevationmodels-usgs-dems/
USDA Imagery and USGS Topographic Imagery (MrSID) https://gdg.sc.egov.usda.gov/
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