Quaternary geologic mapping and aerial photography

Mapping module for Field Geology, Arizona State University

Why?

The Quaternary is the last 1.6 million years. Geologic events that have happened in that time may happen again in the pnear future. If we document the recent history at the earth's surface, we can establish plausible scenarios for the future. In other words, the highest floods along the Salt River in the last 10s to 100s of thousands of years probably give a measure of the highest ones to expect in our lifetime. Or, if we map a series of geologic units, some cut by a fault and some uncut by a fault, we can establish when the fault last ruptured. If those units are late Quaternary or Holocene (the last 10 thousand years), we can probably say that the fault is still active. So, mapping landforms and young deposits identifies the processes and the materials on which human and other biologic activities depend and influence.

How?

The basic idea of mapping Quaternary units is the same as other mapping, we just open our eyes more to the landforms as well as the different sedimentary units. We identify mappable units by their position in the landscape, the kind of processes that operate over them, their history since deposition, etc. In particular, the history of materials after their deposition may include the formation of soils in their uppermost levels (a few m). We can use the degree of soil formation (carbonate and clay accumulation for example) to determine a relative age for different surfaces in our map area.

Scale

If your pencil tip is 0.5 mm in diameter, how big on the ground is it if you are mapping on a 1:24,000 scale map?  How about a 1:500,000 map?

Topographic maps

Show distribution of elevation in a region via contours (lines of equal elevation)
1:24,000 scale is typical for many places, but sometimes 1:200,000 or smaller is all that is possible.

Aerial Photography

Form of remote sensing and powerful tool for many geomorphic investigations

Mapping and image interpretation

Basic Elements of Air Photo Interpretation

--From U. Texas link
"Novice photo interpreters often encounter difficulties when presented with their first aerial photograph. Aerial photographs are different from "regular" photos in at least three important ways:
1) objects are portrayed from an overhead (and unfamiliar) position.
2) very often, infrared wavelengths are recorded, and
3) photos are taken at scales most people are unaccustomed to seeing

These "basic elements" can aid in identifying objects on aerial photographs.

Tone (also called Hue or Color) -- Tone refers to the relative brightness or color of elements on a photograph. It is, perhaps, the most basic of the interpretive elements because without tonal differences none of the other elements could be discerned.
Size -- The size of objects must be considered in the context of the scale of a photograph. The scale will help you determine if an object is a stock pond or Lake Minnetonka.
Shape -- refers to the general outline of objects. Regular geometric shapes are usually indicators of human presence and use. Some objects can be identified almost solely on the basis of their shapes.
-the Pentagon Building
-(American) football fields
-cloverleaf highway interchanges
Texture -- The impression of "smoothness" or "roughness" of image features is caused by the frequency of change of tone in photographs. It is produced by a set of features too small to identify individually. Grass, cement, and water generally appear "smooth", while a forest canopy may appear "rough".
Pattern (spatial arrangement) -- The patterns formed by objects in a photo can be diagnostic. Consider the difference between (1) the random pattern formed by an unmanaged area of trees and (2) the evenly spaced rows formed by an orchard.
Shadow -- Shadows aid interpreters in determining the height of objects in aerial photographs. However, they also obscure objects lying within them.
Site -- refers to topographic or geographic location. This characteristic of photographs is especially important in identifying vegetation types and landforms. For example, large circular depressions in the ground are readily identified as sinkholes in central Florida, where the bedrock consists of limestone. This identification would make little sense, however, if the site were underlain by granite.
Association -- Some objects are always found in association with other objects. The context of an object can provide insight into what it is. For instance, a nuclear power plant is not (generally) going to be found in the midst of single-family housing. "

Stereoscopic viewing

IC Power controls 3D aerial photography (nice demo of stereo viewing)

Geomorphic mapping

Very important means of establishing landforms, their distributions and relations to eachother, process distribution, and history.

Quaternary Geologic mapping

Emphasis on young deposits and landforms that are usually lumped into one unit in bedrock mapping. Uses both the deposit ccharacteristics as well as the landform shape and position in the landscape as criteria for unit designation.
I can't work on anything unless I map it first!

Ramon's Mapping Mantras

1) Even coverage: if there is a blank space, you did not look there.
2) Strive to provide detail. ;Do not generalize.
3) All lines mean something.
4) Consistent notation and symbology.
5) Quality control. Dashing, line wts, queries. Don't be wishy washy, but if something is uncertain or approximate, indicate so.
6) Data/Ink ratio -> 1. Put emphasis on important things (data) by putting relatively more ink in them--higher line weights, larger text, etc.)
7) Neatness counts. Get some nice tools.

Edward R. Tufte and visualizing information

Check out this link from the computers in geology class (http://geology.asu.edu/~glg410/Lectures/GLG410-charting.html)

Photogrammetry and digital imagery

This is the direction things are going. Points made above apply.
Look at this link for some advanced stereographic analysis by one of the students in my research group:
http://activetectonics.la.asu.edu/carrizo/DBmovies.html

Reference links

Nice pages from the University of Wisconsin with the basics of aerial photography
Aerial Imagery Guidelines
Kite Photography at ASU

Assignment to prepare for Salt River mapping exercise

Using the two stereo photos and the glasses we have provided, make a geomorphic map of the area of overlap between the two photos. Use the suggested map symbols below as a start. Produce your map on the mylar we have provided.
Questions to consider:
What are the main processes that move material in this landscape?
What is the erosional and depositional history here?
How does the landscape around the Salt River respond to downcutting along the Salt River? Here is the link to the suggested map patterns:
Map patterns
Here are some different views of the site:
View 1--oblique view to the southeast
View 2--DEM
View 3--draped aerial photograph over DEM

Here is a movie of a flythrough made (as the above are) with Microdem. It is an *.AVI file (you can view it with the Windows Media Player for example), but watch out it is 54Mb!
Movie


Page maintained by
Ramon Arrowsmith

Last update February 23, 2001