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 (~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

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:

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:

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