1. Describe the bathymetry of the ocean seafloor and how the features relate to plate tectonics.
The term bathymetry referred to the ocean’s depth relative to sea level, or the depths and shapes of underwater terrain.
In the same way that topographic maps represent the three-dimensional features of overland terrain, bathymetric maps illustrate the land that lies underwater. Variations in sea-floor relief may be depicted by color and contour lines called depth contours or isobaths.
The ocean floor is not just a vast expanse of flat rock and sand covered with water. In fact, bathymetric features rising from the ocean floor are just as dynamic and diverse as the topography on land. The ocean has mountain ranges, volcanoes, trenches, canyons, and a host of other complex three-dimensional structures.
Just as there are three-dimensional structures and features on the seafloor, there are three-dimensional features in ...view middle of the document...
Since the plates on either side of a transform boundary are merely sliding past each other and not tearing or crunching each other, transform boundaries lack the spectacular features found at other types of boundaries. Instead, transform boundaries are marked in some places by valleys along the boundary where rock has been ground up by the sliding. In other places, transform boundaries are marked by features like stream beds that have been split in half and the two halves have moved in opposite directions.
Perhaps the most famous transform boundary in the world is the San Andreas fault. The slice of California to the west of the fault is slowly moving north relative to the rest of California. Since motion along the fault is sideways and not vertical, Los Angeles will not crack off and fall into the ocean as popularly thought, but it will simply creep towards San Francisco at about 6 centimeters per year. In about ten million years, the two cities will be side by side!
Although transform boundaries are not marked by spectacular surface features, their sliding motion does cause lots of earthquakes.
3. Charles Darwin noticed that the geology of the Galapagos Islands suggested that the islands were sinking. Explain what he meant by this statement.
Darwin made important observations about the geology of the islands and coastlines he visited. He proposed a theory about the formation of atolls. Atolls are coral reefs that form small islands that enclose a lagoon. They are found mostly in the Pacific. Darwin proposed that the foundation for the atoll was a volcano that was sinking because of its weight. As the volcano sinks, coral reefs that rim the volcano grow upwards. As long as the rate at which corals grow kept up with how fast the island was sinking, then small coral islands would remain in a ring around the now sunken volcano.
The central idea of his theory, as it was later formulated, was that the islands were formed by the upward growth of coral as the Pacific Ocean floor gradually subsided.
Plate Tectonics and the Formation of the Galapagos Islands |