Aerial Photography for Geologic Mapping and Analysis

1. Aerial Photography for Geologic Mapping and Analysis

2. Astronaut Video: Sarychev Volcano Eruption

3. Application of air photos to… • Lithology – rock type of surface rocks and bedrock • Structure – folding, faulting and deformation of rocks • Landform – terrain features formed by natural processes that appear similar wherever they are found (Way 1973); Can be erosional or depositional • Drainage pattern – the aggregate of flow channels regardless of whether water is in them now • Soils – soil types as expressed on the surface and organized into standard classification schemes

4. Devil’s Tower (Igneous rock protruding from eroded sedimentary strata) (Air Photo Courtesy Louis Maher, Jr.)

5. Lithological Units • Igneous - rock formed directly from molten mass: intrusive (granite) or extrusive (basalt) are common examples. • Sedimentary – sediment deposited and lithified (turned to rock) after being transported by water, wind and/or gravity: sandstone, siltstone, shale, limestone are common examples • Metamorphic - formed by action of heat or pressure on previously existing rock: gneiss, schist, slate, and quartzite are common examples

6. 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.)

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

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

9. Mapping lithology with air photos. • Lithology is an important aspect of geologic mapping • Interpretation of lithology 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 must be trained to understand these relationships on photos and in the field

10. Climate • 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.

11. Drainage patterns • 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

12. Drainage patterns A. Dendritic B. Parallel • 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.gifOriginally from Howard, 1967

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

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

15. Igneous rocks on air photos: Basalt flow example • 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.)

16. Sedimentary rocks on air photos: Example – sandstone in arid climate • 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.)

17. Geologic Structure • 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

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

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

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

24. Mapping and analyzing geologic structure with air photos • 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

25. Geologic map of Wyoming’s Casper Arch (Image Courtesy NASA.)

26. Geologic structure in California (Image Courtesy of NASA)

27. Landforms and Geomorphology • 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

28. Broad categories of landforms • 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)

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

30. Great Sand Dunes, Colorado (Air Photo Courtesy Louis Maher, Jr.)

31. Mapping and analyzing landforms with air photos • 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.

32. Soils • 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

33. Examples of soil map order 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

34. Soil survey on air photo (From Wikipedia)

35. Summary • 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