Coastal Plain Physiography Topics

1. Regional Setting
2. General Physiography
3. Beaches and Shores
Sea Level Changes
Environ-ments
4. Special Features
• Introduction to Physiography
• Coastal Plain
• Piedmont
• Mesozoic Basins
• Blue Ridge
• Valley and Ridge
• Appalachian Plateaus
• Virginia's Rivers

 

Beaches and Shores, Part 2

Sea Level Changes (continued)

Tides

• In most places, tides rise and fall twice per day.

• Tides are caused by the gravitational forces of the earth, the sun, and the moon, and the rotations of the earth-moon system.

Low tide on the Eastern Shore. High tides and low tides move back and forth across shorelines approximately twice a day. (Photograph by Stan Johnson)

• Every two weeks, tides go through a cycle called the astronomical tide.

• When the sun, the moon, and the earth line up (at full moon and at new moon), high tides are higher and low tides are lower.  This is called spring tide.

Spring tide is caused by the pull of gravities from the sun and the moon (on either side of earth) lining up. Spring tide occurs with the full moon or the new moon. (Figure courtesy of the Virginia Institute of Marine Science)

• When the sun, the moon, and the earth are at a right angle (at first or third quarter moons), high and low tides do not rise or fall as much as other times.  This is called neap tide.

Neap tide is caused by the pull of gravities from the sun and the moon (on either side of earth) pulling at right angles to each other. Neap tide occurs at first and third quarter moons. (Figure courtesy of the Virginia Institute of Marine Science)

• Some types of currents are associated with rising and falling tides.

Graph of flood and ebb tides showing slack tide in between. Maximum flood and ebb currents can be very strong and can create unsafe conditions in some areas along the coast. (Figure courtesy of the Virginia Institute of Marine Science)

• Flood currents are associated with the rising tide.

• Ebb currents are associated with the falling tide.

• The time when water is neither rising nor falling is called slack tide.