Textbook for geologists (2002)

Geologic map of the Sheep Mt. Anticline, Wyoming, based on air photos. From Banjeree and Mitra AAPG Bulletin 88(9):

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 1 st through 5 th 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??

Igneous Rocks (basalt flows) at Craters of the Moon, ID (Air Photo Courtesy Louis Maher, Jr.) What kind of rock is this? What clues are you using?

Sedimentary Rocks (badlands) in South Dakota (Air Photo Courtesy Louis Maher, Jr.) What kind of rock?

Metamorphic Rock from Grand Canyon (not an air photo!) (Courtesy American Geological Institute) What kind of rock? What’s the scale of this photo?

Lithology is an important aspect of geologic mapping Interpretation from air photos requires knowledge of relationship between the lithology and: 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

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 A. DendriticB. Parallel

Rectangular drainage on Volga River (caused by faulting) (Satellite image) What kind of drainage is this? What causes it?

Dendritic drainage pattern (Photo courtesy Michael Collier) Type of drainage?

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 Sedimentary rocks (sandstone) at Castle Valley, UT (Air Photo Courtesy Louis Maher, Jr.) Where is this? Can you name these features?

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: Strike and dip Folds (e.g., anticlines, synclines, domes, basins, etc.) Faults (e.g., normal, reverse, horst and graben, etc.) Joints Unconformities

Sheep Mountain anticline in Bighorn Basin of Wyoming (Air Photo Courtesy Louis Maher, Jr.) Can you name this Wyoming feature?

Sandstone jointing in Arches National Park (Air Photo Courtesy Louis Maher, Jr.) Type of rock? What are the linear features?

Angular Unconformity (Photo by James St. John, Flickr Creative Commons, flickr: jsj1771) What is this called?

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 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)

Glacial moraine near Pinedale, Wyoming (Air Photo Courtesy Louis Maher, Jr.) What kind of landform? Where?

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 1 st order surveys are most detailed and 5 th order are least Lower (1 st, 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 level1 st order1:8,000 scale Detailed soil map2 nd order1:20,000 scale Soil association map 4 th order1:250,000 scale Statewide soil map5 th order1:1,000,000 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