1. Is the WA/OR coast at an active or passive continental margin? Explain. 2. Wo
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Question
1. Is the WA/OR coast at an active or passive continental margin? Explain.
2. Would you call the WA/OR coast a primary or secondary coast? Explain.
3. Briefly describe the difference between the BC coast and the WA/OR coast as follows:
a. Which section of the Pacific NW (BC or WA/OR) has the greater input of river water and sediments? Explain.
b. Which section of the Pacific NW (BC or WA/OR) has the most rugged coastline, much like that of SW Ireland and SW New Zealand? Why do you think this is the case?
Explanation / Answer
1. An active continental margin is found on the leading edge of the continent where it is crashing into an oceanic plate. An excellent example is the west coast of South America. Active margins are commonly the sites of tectonic activity: earthquakes, volcanoes, mountain building, and the formation of new igneous rock. Because of the mountainous terrain, most of the rivers are fairly short, and the continental shelf is narrow to non-existent, dropping off quickly into the depths of the subduction trench.
2. Primary coasts happen because of changes in the land, ... River deltas are an example of a primary coast.
3a. Fraser River section
b)
The lowlands of Oregon are part of a structural trough that was created when that area sank at the same time that the Cascades to the east were elevated. This trough extends northward in the form of straits separating Canada's Vancouver Island from the rest of British Columbia, then passes through the complex of islands that line the Alaska Panhandle and provides the Inside Passage north as far as Juneau.
Farther inland, the Cascades extend from the Klamath Mountains northward into southern British Columbia. The southern section of these mountains appears as a high, eroded plateau topped by a line of volcanic peaks. Between Mount Lassen in California (one of the few volcanoes in the United States to have been active in historic time) and Mount Hood in Oregon, these peaks are especially splendid in their isolation above the surrounding plateaus. The northern Cascades are more rugged and have long proved a difficult barrier to movement eastward from the populous Puget Sound lowland. Here, extinct volcanoes, most notably Mount Rainier, provide the highest elevations and best defined peaks.
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