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!

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.

Explanation / Answer

Secondary-type Coastline:-“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. The two coastal areas under this type are:-

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.

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 like that of Norway; a drowned coastline of former glacial troughs and river valleys.

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