A. Which of the 7 coastal areas above (Ireland, New Zealand, Baja West Coast, Ba

Question

A. Which of the 7 coastal areas above (Ireland, New Zealand, Baja West Coast, Baja East Coast, Yucatan, Cape Cod, BC Canada) could be classified by the following terms? Be sure to explain each of your choices! 1. Active plate margin: At this type of margin, plate tectonic motions are present nearby (within a few hundred kilometers); for example, a subduction zone creates an active plate margin with a relatively narrow continental shelf because oceanic and continental sediments are deposited into the trench and become part of the subduction process. Also, a nearby rift zone can create an uplifted coastal region; this is a different kind of active plate margin than a subduction zone and does apply to one of the areas above! Which 3 coastal area(s) can be classified as being close (within a few 100 km) to an Active Plate Margin? Explain each. a. b. c. 2. Passive plate margin: At this type of margin, plate motions are far from the coastline, so the sediments accumulate both vertically and horizontally, creating a broader shelf with deep sediment layer. Which 4 coastal area(s) can be classified as being far from (more than 100 km) to an Active Plate Margin, and therefore considered to have a Passive Plate Margin? Explain each. a. b. c. d. 3. Primary-type coast: “Primary” refers to the fact that processes such as river input, coastal uplift, or coastal sinking, dominate the coast, and that re-working of the shore by wave action is not yet well developed. The types of sediments most likely found would represent the continental rock composition, and the degree of their sorting and rounding would be less. Which 3 coastal area(s) can be classified as having a Primary-type Coastline? Explain each. Ignore the E and W Baja coasts. a. b. c. 6. Secondary-type coast: “Secondary” refers to the fact that the dominant process now affecting the coastline is wave action, which erodes headlands and deposits sediment and sand. Longshore current and drift moves beach sand along the coast longitudinally, and storms bring up sediments from the continental shelf. Sands may be more rounded and well-sorted. Which 2 coastal area(s) can be classified as having a Secondary-type Coastline? Explain. Ignore the E and W Baja coasts. a. b. B. Do a Google or other web search for images and maps of the continuous coastline of Washington and Oregon. Define this coastline in terms of the above categories as follows: 7. Is the WA/OR coast at an active or passive continental margin? Explain. 8. Would you call the WA/OR coast a primary or secondary coast? Explain. 9. 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. Ireland- Most of Ireland was formerly part of eastern US and Canada. It was moved to its present location as a result of the breakup of Pangaea (opening of the mid-Atlantic). Massive limestone from an ancient ocean basin makes up much of the west side and Atlantic coast, and produced the Cliffs of Moher and The Burren. The basalt columns of Giants Causeway in the northeast are the result of rifting about 65 million years ago; they are also found across the sea to the southwest of Scotland. The climate is kept mild by the influence of the Gulf Stream ocean current, bringing warmer water from the tropics.

These are Active plate margin . (Plate tectonic motions are present nearby; for example, a subduction zone creates an active plate margin with a relatively narrow continental shelf because oceanic and continental sediments are deposited into the trench and become part of the subduction process. A nearby rift zone can create an uplifted coastal region.)

These are also Emergent Coastline (Either the coastline is rising due to isostatic processes (rebounding after removal of glacial weight) or tectonic processes (crustal compression and uplift), or sea level is dropping, or both. This process exposes coastal seafloor, such as wave cut terraces and platforms)

These are Primary-type coast (“Primary” refers to the fact that processes such as river input, or coastal uplift, or subsidence, dominate the coast, and that re-working of the shore by wave action is not yet well developed. The types of sediments most likely found would represent the continental rock composition, and the degree of their sorting and rounding would be less.)

2. NEW ZEALAND: New Zealand straddles a subduction zone between the Pacific and Australian plates; where subduction is going in two opposite directions, stretching New Zealand with it. North Island rides atop the NW-moving Pacific Plate which is subducting beneath the Australian Plate. South Island is mostly in the tear-apart (transform or strike slip) fault zone, but further the south the SE-moving Australian plate subducts beneath the Pacific Plate. The climate is mild; warmer to the north and more seasonal to the south.

These are Active plate margin (Plate tectonic motions are present nearby; for example, a subduction zone creates an active plate margin with a relatively narrow continental shelf because oceanic and continental sediments are deposited into the trench and become part of the subduction process. A nearby rift zone can create an uplifted coastal region.)

These are Submergent Coastline (Either the coastline is subsiding due to tectonic processes (crustal extension or thinning), or sea level is rising, or both. This is characterized by fjords (drowned glacial troughs), drowned river valleys, and numerous islands and inlets.)

These are Primary-type coast (“Primary” refers to the fact that processes such as river input, or coastal uplift, or subsidence, dominate the coast, and that re-working of the shore by wave action is not yet well developed. The types of sediments most likely found would represent the continental rock composition, and the degree of their sorting and rounding would be less.)

3. BAJA PENINSULA (Mexico): During the breakup of Pangaea (beginning about 200 million years ago), the North American plate collided with the fast-moving Farallon plate to its west. A subduction zone formed, and with it, the subsequent spine of granitic mountains that make up most of Baja’s structure and landscape. Even further west, the East Pacific Rise spreading ridge separated the Farallon Plate from the Pacific plate; it ultimately subducted as well. Heat from the subducted East Pacific Rise weakened the continental crust and created a rift zone that we now see as the floor of the Sea of Cortez, ultimately separating Baja peninsula from the Mexican mainland like an opening zipper, from south to north. With the disappearance of the Farallon/Pacific spreading ridge, the boundary between the North American plate to the east and the NW-heading Pacific plate to the west became the transform (strike slip) boundary of the San Andreas Fault system. The opening was complete and the sea rushed in to fill it roughly 5 million years ago, and the Sea of Cortez was born. Baja California and the part of California west of the San Andreas fault, riding on the NW-moving Pacific Plate, will tear off the continent entirely and become a very long island, en route to the Aleutian Trench of SW Alaska in about 50 million years.

These are Active plate margin( Plate tectonic motions are present nearby; for example, a subduction zone creates an active plate margin with a relatively narrow continental shelf because oceanic and continental sediments are deposited into the trench and become part of the subduction process. A nearby rift zone can create an uplifted coastal region.)

These are Emergent Coastline(Either the coastline is rising due to isostatic processes (rebounding after removal of glacial weight) or tectonic processes (crustal compression and uplift), or sea level is dropping, or both. This process exposes coastal seafloor, such as wave cut terraces and platforms.)

These are also Primary-type coast(“Primary” refers to the fact that processes such as river input, or coastal uplift, or subsidence, dominate the coast, and that re-working of the shore by wave action is not yet well developed. The types of sediments most likely found would represent the continental rock composition, and the degree of their sorting and rounding would be less.)

4. YUCATAN PENINSULA (Mexico): From about 100 million years ago to about 2 million years ago, much of the Yucatan was submerged under warm shallow seas, at which time over 2300 meters of limestone strata, created by coral reefs and seawater-precipitated limestone, was deposited. Over 150 cm of rainfall per year falls here, to which atmospheric carbon dioxide lends a slight acidity. The limestone is very porous, and this acidic rainfall rapidly percolates towards a shallow freshwater table. Steering a course to the Caribbean through bedding fractures, this acidified water has dissolved conduits (caves) in the parent limestone since its initial uplift from the ocean. Falling sea levels during active glaciation (2 million to about 10,000 years ago) resulted in a considerable drop in the water table and thus, loss of water in the drainage channels. Unsupported cave ceilings near the surface collapsed creating caves, caverns and surface sinkholes at odd intervals along the course of the conduits. About 10,000 years ago sea level began to rise from 125 m below its present level, raising the freshwater table. Deeper caverns were flooded by seawater and surface caverns were flooded by freshwater. The Mesoamerican Reef, 2nd largest reef in the world after the Great Barrier Reef, is the southeastward extension of the Yucatan carbonate platform.

These are Passive plate margin (Plate motions are far from the coastline, so the sediments accumulate both vertically and horizontally, creating a broader shelf with deep sediment layer.)

These are Submergent Coastline (Either the coastline is subsiding due to tectonic processes (crustal extension or thinning), or sea level is rising, or both. This is characterized by fjords (drowned glacial troughs), drowned river valleys, and numerous islands and inlets. )

These are Secondary-type coast (“Secondary” refers to the fact that the dominant process now affecting the coastline is wave action, which erodes headlands and deposits sediment and sand. Longshore current and drift moves beach sand along the coast longitudinally, and storms bring up sediments from the more distant continental shelf. Sands may be more rounded and well-sorted.)

5. CAPE COD: The geologic history of Cape Cod mostly involves the advance and retreat of the last continental ice sheet (named the Laurentide after the Laurentian region of Canada where it first formed) and the rise in sea level that followed the retreat of the ice sheet. The sandy peninsula is the remnant of a huge terminal moraine, formed within the past 25,000 years. It remains an area of great geological interest because of its recent formation, and the effect that rising sea level is having on the sandy margins.

These are Passive plate margin( Plate motions are far from the coastline, so the sediments accumulate both vertically and horizontally, creating a broader shelf with deep sediment layer.)

These are Submergent Coastline: Either the coastline is subsiding due to tectonic processes (crustal extension or thinning), or sea level is rising, or both. This is characterized by fjords (drowned glacial troughs), drowned river valleys, and numerous islands and inlets.

6. BRITISH COLUMBIA, CANADA: The geology of BC (and the rest of the Pacific Northwest) is too complex. Suffice to say, most of the landscape from Alaska to California, and from the Pacific coast to the western edge of the Rockies either originated somewhere else, or formed in place as the “stuff from somewhere else” collided with ancestral North America. The BC coast of Canada is a drowned coastline of former glacial troughs and river valleys.

These are Passive plate margin Plate motions are far from the coastline, so the sediments accumulate both vertically and horizontally, creating a broader shelf with deep sediment layer.

These are Submergent Coastline (Either the coastline is subsiding due to tectonic processes (crustal extension or thinning), or sea level is rising, or both. This is characterized by fjords (drowned glacial troughs), drowned river valleys, and numerous islands and inlets.)

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