Lecture 22

Question 1

Tides

Answer 1

Sea level rises and falls twice in just over 24 hours; monthly variation too.

Question 2

Causes of tides

Answer 2

Caused by rotation of earth and gravitational attraction of Moon and Sun.
Moon ore important (less mass, but closer to Sun).
Sun can add or subtract from tides.

Question 3

Spring tide

Answer 3

Sun and moon align and make highest tide of the moon - full and new moon.

Question 4

Neap tide

Answer 4

Sun, Earth, and Moon make right angle, so lowest tides of the month - quarter moon.

Question 5

Ice ages and sea level

Answer 5

Longer term effect of sea level changes is ice ages when more water is stored on land, so less in oceans (sea level drops). Alters location of coast.

Question 6

Tectonic uplift

Answer 6

Like West Coast of NA - relative drop in sea level.

Question 7

Subsidence

Answer 7

Like Gulf Coast - relative rise in sea level.

Question 8

Wind waves

Answer 8

Only extend to depth of about one-half wavelength.

Question 9

Size of waves

Answer 9

Determined by wind speed, wind duration, and fetch (distance wind blows over water). largest waves about 30 meters high.

Question 10

Tsunamis

Answer 10

Different kind of wave, caused by earthquake, landslide, volcano. Low height over deep water, very high at coast; often highly destructive.

Question 11

Wave breaking

Answer 11

In shallow water, wave deforms bc it is in contact with sea floor.
Breaking; wave falls over bc too steep. Water runs up the beach, runs out of energy, and gravity pulls it back into ocean.

Question 12

Wave refraction

Answer 12

Bending of waves as they approach the shore. Generally approach at an angle to beach, so one part of waves touches sea floor before rest. Refracted bc one side slowed before other.

Question 13

Littoral drift

Answer 13

beach drift + longshore drift.

Question 14

Beach drift

Answer 14

Water and sand rush up beach at angle, return straight down; net movement down beach.

Question 15

Longshore drift

Answer 15

Longshore current (buildup of water at beach, current of water parallel to shore) acts like stream, carrying sand.

Question 16

Wave cut platforms

Answer 16

Base of cliff erodes, so cliff falls down and cliff moves back over time. Wave cut platform develops at sea level where cliff used to be.

Question 17

Marine terraces

Answer 17

Platforms elevated above sea level.

Question 18

Headlands and their erosion

Answer 18

Headlands are bedrock jutting out from coast.
Refraction causes waves to hit sides.
Erosion, especially along cracks, leads to distinctive landforms. (Caves, arches, stacks).

Question 19

Winter beach

Answer 19

Season of big waves. Sand eroded off beach and deposited offshore - small beach.

Question 20

Summer beach

Answer 20

Season of small waves. Sand pushed back onto beach - broad beach.

Question 21

Spit

Answer 21

At indention in coast, sand grows out into the water.

Question 22

Tombolo

Answer 22

Spit connects mainland and island.

Question 23

Barrier beach

Answer 23

Drifting sand blocks stream mouth.

Question 24

Humans modify littoral drift

Answer 24

To keep a spit from blocking a bay, a dredge may be used to move the sand.
Groins and jetties are used to build up beaches, but often cause erosion elsewhere.
Seawalls built to absorb energy of waves, but may cause erosion on seaward side.
Beach nourishment; artificially bring sand to beach. (expensive and temporary).

Question 25

Barrier islands

Answer 25

Narrow islands parallel to mainland.
Common on Gulf and Atlantic Coasts. Protects mainland form big waves.
CHECK DIAGRAM.

Question 26

TX beaches

Answer 26

Net erosion since at least mid 1800s.
Sea level rise and subsidence.
Damming of streams too.
1-2 m of erosion per year.

Question 27

Coral reefs

Answer 27

Formed by accumulation of calcium carbonate from shells of coral. Requires warm and shallows waters, so found in tropical areas. For reefs to get big, the relative sea level must rise, so subsiding coasts.
Fringing reef; connected to land.
Barrier reef; separated from land (land sinking).
Atoll; land underwater, just reef at surface.

Question 28

Submergent coasts

Answer 28

Relative sea level rise (water rises above land).

Question 29

Ria coasts

Answer 29

Drowned stream valleys.

Question 30

Fiord coasts

Answer 30

Sea fills glacial valleys

Question 31

Emergent coasts

Answer 31

Relative sea level drop (land rising above water).