Understanding Azonal and Representative Land Relief

Posted on Nov 15, 2024 in Geology

Azonal Systems

Azonal landforms do not depend on the climate, but on other factors, such as rock composition and tectonic structure.

1. Coastal Morphology

Geologic Agents:

Waves, tides, and sea currents.

Erosion Landforms:

Cliffs, wave-cut platforms, sea arches, and sea stacks.

Deposition Landforms:

Beaches, barrier spits, barrier islands, tombolos (which form the bar of a tied island), and lagoons.

2. Lithological Morphology

Sometimes, certain types of rocks develop special landforms due to their unique properties. Landforms related to specific lithological compositions include karstic and granite landforms.

Karstic Landforms

These landforms develop on soluble rocks, primarily limestone. Calcite is insoluble in pure water but dissolves in water containing carbon dioxide. This dissolution of limestone forms various landforms:

  • Surface Solution Landforms:
    • Karren or lapies
    • Sinkholes
  • Collapse Landforms:
    • Collapse dolines
    • Poljes
  • Underground Landforms:
    • Caves
    • Stalactites
    • Stalagmites

Granite Landforms

Granite is resistant to physical weathering but susceptible to chemical weathering. Mica and feldspar react to become clay minerals, resulting in the formation of clay and loose quartz grains.

  • In plain areas with minimal sand transportation, it remains in situ, forming numerous gentle hills: undulating hills.
  • In mountainous areas where clay and sand are easily removed, chemical weathering progresses along fractures, leaving the core of these blocks untouched. This process forms granite boulders (also called tors).

3. Structural Morphology

Landforms Related to Faulting

  • Tensional Landforms:
    • Horsts and Grabens
    • Tilted Blocks
  • Compressional Landforms:
    • Reverse Faults: Tectonic scales
    • Thrust Faults/Nappes: Tectonic window, klippes

Landforms Related to Folding

When layers of hard and smooth rocks are present, differential erosion exposes the hard layers:

  • Jura-Type (Conform) Relief: Occurs when the topographic and tectonic surfaces are the same. Valleys are formed by synclines, and hilltops are formed by anticlines. When anticlines begin to erode, combes and cluses are formed.
  • Inverted Relief: Occurs when valleys are formed by anticlinal valleys and hills by perched synclines.

Land Relief Representation

Topographic maps depict topography using various techniques, primarily contour lines.

Contour Lines

Contour lines are curves that connect contiguous points of the same altitude.

Contour Interval

The contour interval of a map is the constant elevation difference between successive contour lines.

Scale

In addition to a ratio scale, a bar scale can be included to facilitate distance measurement on the map and conversion to real-world distances.

To visualize land relief effectively using contour lines, consider these three basic rules:

  • The Rule of V’s: V-shaped contour lines indicate valleys, with the channel passing through the point of the V, which points upstream.
  • The Rule of O’s: Closed loops typically represent hills, with the innermost loop being the highest area.
  • The Rule of the Spacing of Contours: Close contours indicate a steep slope, while distant contours indicate a gentle slope.

1. Maps and Topographic Profiles

Topographic profiles represent the shape of the land relief along a line on a map. To draw a profile, follow these steps:

  1. Draw the line along which the profile will be represented.
  2. Place a piece of paper along that line.
  3. Mark the starting and ending points clearly (e.g., A and B).
  4. Make a mark on the paper wherever it crosses a contour line and write down the altitude of each.
  5. Once you have finished marking the contour lines, transfer this information to a horizontal line previously drawn on another paper.
  6. Trace a vertical line on the left side and make a mark for each different contour line that crosses the profile. Ensure that the distance between them reflects the same scale as the map.
  7. Make a small dot over each mark at the corresponding altitude.
  8. Connect the dots to complete the profile.

2. Satellite Photographs

Satellite photographs are valuable tools for studying land relief. By using different wavelengths, various factors such as vegetation or the location of mineral resources can be distinguished. This technique is known as remote sensing.