chapter 1.6
How do we depict Earth's surface?
Common representations of Earth's features:
Topographic maps:
Useful for visualizing landscape and navigating the land.
Utilize contour lines to represent elevation changes.
Shaded relief maps:
Emphasize the shape of the land using light and dark shading.
Effective for visualizing terrain in a three-dimensional context.
Maps enable the quantitative measurement of areas, directions, and steepness of slopes.
How do maps help us study Earth's surface?
Maps as primary portrayal of land surface:
Represent various land surface features including shape, elevation, and materials.
Example of SP Crater in Northern Arizona:
Aerial photography is superimposed over topography to illustrate the spatial relationship between landforms and surface composition.
Key features observed:
Cone-shaped hills (small volcanoes) surrounded by broad, less steep areas.
Dark feature in the center represents a solidified lava flow, indicating recent volcanic activity within the last 5000 years.
SP Crater is a significant geological point observed from various perspectives.
Light gray areas and linear features denote different geological materials and fractures in the landscape.
The region exhibits a relatively dry climate with minimal vegetation, enabling clearer views of landforms.
Features in the topography of SP Crater
Cone-shaped volcanoes:
Formed from fragments of molten rock ejected during volcanic activity.
Aerial photograph of SP Crater:
Highlights steep slopes of the volcano in contrast to surrounding land.
Features to observe:
Larger perspective view allows identification of volcanoes and craters, enhancing understanding of regional geology.
Shaded relief maps and topographic maps
Shaded relief maps:
Simulate light and dark shading to represent land shape.
Depict volcanic hills and stream valleys as major landscape features.
Topographic maps:
Display the elevation of the land surface with contour lines.
Each contour line corresponds to a specific elevation above sea level.
Darker lines (index contours) represent every fifth contour, aiding in pattern recognition.
Spacing of contour lines provides information about slope steepness:
Widely spaced contours indicate flat areas or gentle slopes.
Closely spaced contours indicate steep areas like volcanic slopes.
Shape representation:
Contours bend into 'V' shapes in valleys, indicating elevation coming from higher terrain.
Contours bend outward in ridges, showing convex shapes for higher terrain sections.
Differences in topography
Topographic features are not uniform:
The concept of topography:
Defined as the variation in elevation and landform characteristics across a specific area.
Common terms pertaining to elevation and slope steepness:
Elevation: Height of a feature above sea level.
Measured in meters (m) or kilometers (km), often represented in feet (ft) in the US.
Depth: Vertical distance below sea level (also in meters or kilometers).
Topographic relief: Difference in elevation between two features, measured in meters or feet.
High relief indicates rugged terrain, while low relief denotes flatter areas.
Slope and gradient
Representing topography:
Imaginary slices or profiles through the terrain can illustrate elevation changes visually.
Definition and measurement:
Steep slopes appear with cliffs that sharply drop, while gentle slopes are more gradual.
Steepness of slope:
Described in degrees from the horizontal (e.g., SP Crater has a 26-degree slope).
Gradient:
Expressed as a ratio or fraction, typically denoting the vertical drop over horizontal distance:
A slope of 26 degrees corresponds to a drop of 490 meters over 1,000 meters.
Numerically expressed as .