Ch Tides

Why tides occur Refers to cyclic rise and fall of sea water. Refers to cyclic rise and fall of sea water. Variations in gravitational attraction between the Earth, moon and sun. Variations in gravitational attraction between the Earth, moon and sun.

The Moon Primary factor that controls the rhythm and height of the tides 2 tidal bulges due to gravitational attraction Side of Earth closest to moon - seawater drawn towards moon. Opposite side - bulge produced away from the moon. Timing of tides is related to the Earth’s rotation, and the rotation of the moon around the Earth.

The Sun The second factor controlling the tides is the sun’s gravity. The second factor controlling the tides is the sun’s gravity. Average solar tide = half average lunar tide. Average solar tide = half average lunar tide. At certain times, the direction of the moon’s gravitational attraction is aligned with the sun’s. The two act together to produce highest and lowest tides of the year. At certain times, the direction of the moon’s gravitational attraction is aligned with the sun’s. The two act together to produce highest and lowest tides of the year.

SPRING TIDES Highest and lowest tides of the year. (sun and moon aligned) Highest and lowest tides of the year. (sun and moon aligned) Occur every days during full and new moon. Occur every days during full and new moon.

NEAP TIDES The gravitational pull of the sun and moon are at right angles to each other. The gravitational pull of the sun and moon are at right angles to each other. Daily tidal variations on Earth are at their least. Daily tidal variations on Earth are at their least. Occur during first and last quarter of the moon. Occur during first and last quarter of the moon.

Tidal bore = a true tidal wave Wall of water that moves upriver Wall of water that moves upriver Caused by an incoming high tide Caused by an incoming high tide Occurs in some low-lying rivers Occurs in some low-lying rivers Can be large enough to surf or raft Can be large enough to surf or raft

TYPES OF TIDES Geometric relationship of sun and moon to locations on the Earth’s surface creates three different types of tides. Geometric relationship of sun and moon to locations on the Earth’s surface creates three different types of tides. 1. DIURNAL TIDES: one high and one low water tidal per day. Northern Gulf of Mexico and SE Asia.

2. SEMI-DIURNAL TIDE: Two high and two low waters per tidal day. Common on Atlantic coasts of the United States and Europe.

3. MIXED TIDES: Successive high-water and low-water stands differ appreciably. Successive high-water and low-water stands differ appreciably. Higher high water and lower high water, as well as higher low water and lower low water. Higher high water and lower high water, as well as higher low water and lower low water. West coast of Canada and the US. West coast of Canada and the US.