View
225
Download
0
Category
Preview:
DESCRIPTION
Key Terms Slipface: a steeply sloping surface on the lee side of the dunes standing at or near the angle of repose for loose sand Angle of Repose: the maximum angle of a slope of a certain material before it loses stability (~34 0 ) Ground Penetrating Radar (GPR): a non-invasive geophysical tool/method used to gather detailed information about the subsurface Saltations: Sediment transport where particles are moved forward in a series of short leaps or bounces Foreset: Inclined layers of a cross-bedded unit Bedding: An arrangement of sedimentary rock in layers; the general character or pattern of the beds Paleoflow: a flow direction of sediment preserved in bedrock and determined by examination of sedimentary structures and textures in the rock formed at the time
Citation preview
ICL
Sand dunes to Sandstone: Revealing the Secrets of Zion’s Navajo Sandstone
Organization
• Key terms: concepts you’ll need to know• Activity 1: Interpreting active aeolian dunes• Activity 2: Difficult Dunes and GPR• Activity 3: Uniformitarianism (present is the
key to the past): Zion’s Navajo Sandstone• Activity 4: Comparing field & GPR
interpretations to USGS-developed models
Key Terms• Slipface: a steeply sloping surface on the lee side of the dunes standing
at or near the angle of repose for loose sand• Angle of Repose: the maximum angle of a slope of a certain material
before it loses stability (~340)• Ground Penetrating Radar (GPR): a non-invasive geophysical
tool/method used to gather detailed information about the subsurface• Saltations: Sediment transport where particles are moved forward in a
series of short leaps or bounces• Foreset: Inclined layers of a cross-bedded unit
• Bedding: An arrangement of sedimentary rock in layers; the general character or pattern of the beds
• Paleoflow: a flow direction of sediment preserved in bedrock and determined by examination of sedimentary structures and textures in the rock formed at the time
Paleoflow & Slipface
Activity 1
• Background: using theory to interpret observations, or vice-versa– In geomorph, link knowledge of process with
observations of landforms• Instructions: Use your knowledge of aeolian
processes to interpret different types of aeolian dune landforms• Remember this?...
Activity 2
• Task 1: Analysis of the topographic map to located similar landforms
• Task 2: Interpreting the GPR image• Task 3: How did these possible dunes form
and why are they not still moving?
Activity 3
• Task 1: Virtual Fieldwork: interpreting photographs
• Task 2: Using GPR to investigate the field site
Activity 4
• Task 1: Your field site description
• Task 2: Which model works best?– Models from USGS website:• http://walrus.wr.usgs.gov/seds/bedforms/pindex.html
Activity 1 Questions
• Which side of the photograph is the lee facing (left, up, right, down)?
• What is the sand’s source—from which side of the photograph is the dominant wind direction?
• What types of dune are these?• What observations led you to this conclusion?
Activity 2
• Difficult Dunes and GPR• Interpret GPR imagery by making measurements
of slope angle• Analyze possible processes involved in possible
dune formation & stabilization
Activity 2, Task 1
• Analysis of the topo map to locate similar landforms– Do you see any other locations of possible sand
dunes in the vicinity of the red oval on the Eau Claire topo map? How many?
Activity 2, Task 2
• Interpreting the GPR image– Geo-nerds love anomalies!– Once anomalies are determined, hypotheses can
be created; Small hills on topo map could be…• Drumlins? Kames? Glacial till? Erosional stream
remnants?
– If these “hills” are aeolian dunes, then angle of repose would be reflected in the slip face
Activity 2, Task 2 (cont.)
• Measure the angle of repose on the GPR image– Protractor (easiest)
OR“rise over run”• Rise = vertical change of slip face; run = horizontal
position– Each tiny “tick” ~0.1m on the horizontal scale and ~0.08m on
the vertical scale– Online here: www.1728.com/distance
Activity 2, Task 3
• Determining the internal structure of the possible Roy Street San Dunes– Possible sand source– Possible saltation from source to location– How sand was stabilized
• Must know wind direction first
Activity 3• Uniformatarianism at Zion National Park• Activity 3, Task 1– Examine ancient sand dunes of Navajo formation– Annotate an image
• Activity 3, Task 2– Use GPR imagery to peer into subsurface• Annotate image• Calculate angle of repose• Answer questions associated with dune “packages”
Activity 4
• Comparing your “field” and GPR analysis with USGS-developed models
• Activity 4, Task 1– Field site description
• Activity 4, Task 2– Choosing a model that fits your analysis
Recommended