Overview
This lecture covers earthquake hazards, types of folds, and introduces topographic maps and map reading skills, including concepts of latitude, longitude, and map scales—important for the current lab and test.
Earthquake Hazards
- Divergent boundaries cause tension stress, normal faults, and strike-slip faults.
- Convergent boundaries cause compressional stress, creating reverse or thrust faults.
- Transform boundaries cause shear stress, leading to strike-slip faults.
- Liquefaction occurs when seismic waves liquefy water-filled sediment, reducing friction and stability.
- Liquefaction can cause quicksand (in sand) or quick clay (in clay), leading to dangerous ground conditions.
- Sand volcanoes may form from pressurized water and sand escaping through cracks.
- Tsunamis are large waves caused by underwater earthquakes, landslides, or displacement—dangerous near coasts.
Folds in Rocks
- Folds are created by ductile deformation under compressional stress.
- Anticline: fold that arches upward (convex up, "A" shape).
- Syncline: fold that arches downward (convex down, "Y" shape).
- Overturned folds occur when folding is extreme, sometimes forming recumbent folds.
- Domes have the oldest rocks in the center; basins have the youngest in the center.
Topography & Map Reading
- Cartography is the science of map making; topography is the study of land shapes.
- Topographic maps use contour lines to represent elevation.
- Hillshade techniques use shadows for 3D visualization of landscapes.
- Declination is the difference between true north and magnetic north, important for compass use.
- Map scale indicates the ratio between distances on the map and in real life.
Latitude, Longitude, and Coordinate Systems
- Latitude measures degrees north or south of the equator (0°–90°); longitude measures east or west of the prime meridian (0°–180°).
- The prime meridian (0° longitude) is based at Greenwich, England.
- Time zones are established with respect to the prime meridian and the International Date Line (180°).
- Coordinates can be expressed in degrees, minutes, and seconds or decimal degrees.
- UTM (Universal Transverse Mercator) divides the globe into zones for accurate mapping.
Contour Lines & Elevations
- Contour lines connect points of equal elevation; the contour interval is the vertical distance between lines.
- Close contour lines indicate steep slopes; widely spaced lines indicate gentle slopes.
- Index contours are bolded every fifth line for reference.
- Contour lines form V-shapes pointing upstream in valleys.
- Depressions are shown with hachured contour lines.
- Relief is the elevation difference between two points; total relief is the highest minus the lowest point on a map.
Gradient and Unit Conversion
- Gradient (slope) is calculated as rise/run (vertical/horizontal distance).
- Unit conversions may be needed for measuring slope (e.g., feet to miles).
- Dimensional analysis helps convert units to ensure a pure number for gradient.
Benchmarks
- Benchmarks are marked points with known exact elevation, useful for map-based orientation and triangulation.
Key Terms & Definitions
- Liquefaction — Process where seismic shaking causes water-filled sediments to lose strength and act like a liquid.
- Anticline — Upward-arching fold in rock layers.
- Syncline — Downward, trough-like fold in rock layers.
- Topographic Map — A map showing elevation and land features using contour lines.
- Latitude — Measurement in degrees north or south of the equator.
- Longitude — Measurement in degrees east or west of the prime meridian.
- UTM — Universal Transverse Mercator, a grid-based map coordinate system.
- Contour Line — A line on a map connecting points of equal elevation.
- Declination — The angle difference between magnetic north and true north.
- Relief — The elevation difference between two points on a map.
- Gradient — The measure of the slope (rise over run).
- Benchmark — A reference point with known position and elevation.
Action Items / Next Steps
- Complete the topographic map lab.
- Review the study guide and take the practice test before the exam.
- Prepare and upload your study guide for extra credit.
- Email questions or requests for accommodations to the instructor before the test.