Textbook for geologists (2002)
Geologic map of the
Sheep Mt. Anticline,
Wyoming, based on
air photos.
From Banjeree and Mitra.
2004. AAPG Bulletin
88(9):1227-1237.
 What are the primary applications of aerial
photographs for geologists?
 Be able to define lithology, structure, and landform,
and recognize common examples in air photos.
 How do drainage patterns help us interpret geology?
 How can aerial photography contribute to soil
mapping?
 What do we mean by 1st through 5th order soil maps?
 Lithology
 Structure
 Landforms
 Drainage
 Soils
What do each of these mean??
Devil’s Tower – Lithology?
Structure? Surrounding rock??
(Air Photo Courtesy Louis Maher, Jr.)
Lithological Units
• Igneous
• Sedimentary
• Metamorphic
What are each of these, and what are some
examples??
What kind of rock is this?
What clues are you using?
Igneous Rocks (basalt flows) at
Craters of the Moon, ID
(Air Photo Courtesy Louis Maher, Jr.)
What kind of rock?
Sedimentary Rocks (badlands) in
South Dakota
(Air Photo Courtesy Louis Maher, Jr.)
What kind of rock?
What’s the scale of this photo?
Metamorphic Rock from Grand
Canyon (not an air photo!)
(Courtesy American Geological Institute)
 Lithology is an important aspect of geologic mapping
 Interpretation from air photos requires knowledge of
relationship between the lithology and:
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Climate
Topography
Drainage pattern
Jointing and faulting
Texture
Vegetation
Photointerpretation clues: tone, size, context, shape, etc.
 Photointerpreters should be trained to understand these
relationships on photos and in the field
 Affects the way rocks weather.
 Affects the associations of vegetation with particular
rock types
 Affects soil formation from rock parent material
 Affects erosional patterns
 All of these influence the appearance of different rocks
in photos.
 Drainage patterns are easy to see on aerial
photographs
 Offer clues to many other geologic characteristics of an
area (e.g., topography, bedrock, surface texture and
hardness, jointing, etc.)
 Obvious importance for hydrologic mapping,
modeling and management
 Often influence human land use
A. Dendritic
Drainage patterns
• Dendritic: horizontal sediment or
uniformly (homogeneous) resistant
bedrock; gentle slope
• Parallel: moderate to steep slopes
fine textured deposits or fractured
bedrock or in areas of parallel
elongate landforms
• Trellis: dipping or folded bedrock
• Rectangular: jointed or faulted
bedrock
• Radial: volcanoes, domes, basins
• Annular: domes or basins
• Multibasinal - flat-lying glacial
terrain; karst (limestone) terrain
• Contorted: metamorphic rocks
disc.gsfc.nasa.gov/.../ geo_images_4/Fig4.1.gif
Originally from Howard, 1967
B. Parallel
What kind of drainage is
this?
What causes it?
Rectangular drainage on Volga
River (caused by faulting)
(Satellite image)
Type of drainage?
Dendritic drainage pattern
(Photo courtesy Michael Collier)
 Topography: flat to hilly
 Drainage: parallel or internal
 Photo tone: dark or sometimes spotted
 Gully type: none (not erosive)
Igneous Rocks (basalt flows) at
Craters of the Moon, ID
(Air Photo Courtesy Louis Maher, Jr.)
 Topography: flat or table like (mesas, etc.) but can be
highly eroded
 Drainage: dendritic
 Photo tone: light and banded (can vary considerably)
 Gully type: none to deep depending on steepness
Where is this? Can you name these
features?
Sedimentary rocks (sandstone) at
Castle Valley, UT
(Air Photo Courtesy Louis Maher, Jr.)
 Geologic structures are any features caused by
deformation of rock (folding, faulting, etc.)
 Structure is important for trapping hydrocarbons,
controlling water flow, understanding stratigraphy,
etc.
 Includes:
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Strike and dip
Folds (e.g., anticlines, synclines, domes, basins, etc.)
Faults (e.g., normal, reverse, horst and graben, etc.)
Joints
Unconformities
Can you name this Wyoming
feature?
Sheep Mountain anticline in
Bighorn Basin of Wyoming
(Air Photo Courtesy Louis Maher, Jr.)
Type of rock?
What are the linear
features?
Sandstone jointing in Arches
National Park
(Air Photo Courtesy Louis Maher, Jr.)
What is this called?
Angular Unconformity
(Photo by James St. John, Flickr Creative
Commons, flickr: jsj1771)
 Interpreter looks for changes in tone and texture that
represent boundaries between geologic units
 Works best where vegetation cover is minimal
 But…can sometimes see changes in underlying strata
related to changes in overlying vegetation
 Can sometimes enhance edges with digital filters
 Can use stereo techniques to measure elevation
changes for calculating dip angles
Geologic map of Wyoming’s
Casper Arch
(Image Courtesy NASA.)
Geologic structure in California
(Image Courtesy of NASA)
 Definition of landforms varies with discipline
 Geologist may have different view than soil scientist or
hydrologist
 Creating a landform key is important aspect of aerial
interpretation
 Landforms are strongly influenced by underlying
geology and climate
 Coastal and oceanic (e.g., fjord, ismuth, beach, etc.)
 Erosional landforms (e.g., canyon, cuesta, gully, etc.)
 Fluvial (river related) landforms (e.g., braided
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channel)
Mountain and glacial landforms (e.g., cirque, peak,
etc.)
Slope landforms (e.g., terrace, cuesta, plain)
Volcanic landforms (e.g., cinder cone, lava flow)
Depositional landforms (e.g., alluvial fans)
Etc. (there are many ways to think about landforms)
What kind of landform? Where?
Glacial moraine near Pinedale,
Wyoming
(Air Photo Courtesy Louis Maher, Jr.)
Great Sand Dunes, Colorado
(Air Photo Courtesy Louis Maher, Jr.)
 Identifying landforms on aerial photography uses
many clues
 Topography
 Drainage pattern
 Drainage texture
 Photo tone and texture
 Vegetation patterns
 Land use patterns
 Scale of landform determines scale of imagery
necessary to map. Landforms occur across scales.
 Soils can be mapped at a wide range of scales and
precision
 1st order surveys are most detailed and 5th order are least
 Lower (1st, etc.) order surveys require detail found in air
photos
 Almost all soil mapping requires a combination of
field survey and remote sensing
 Typical project uses manually interpreted aerial
photography followed by field work to label the
interpreted units
Small plot level
1st order
1:8,000 scale
Detailed soil map
2nd order
1:20,000 scale
Soil association map
4th order
1:250,000 scale
Statewide soil map
5th order
1:1,000,000 scale
Soil survey on air photo
(From Wikipedia)
 Aerial photography is widely used for various aspects
of geology
 Choice of air photos depends on scale, spectral
requirements, etc.
 Air photo interpretation for geology usually requires a
coupled field component
 Interpreters must have comprehensive knowledge of a
broad set of indicators that give clues to underlying
geology