Tides are caused by the gravitational pull of the sun and the moon. The moon's pull produces two high tides on the opposite sides of the earth. Some places have a high tidal range. Twice a day the level of the sea will rise or come in and twice a day the level falls or it goes out. The difference in level between high and low water is known as the amplitude of the tide. Winds and the earth's rotation cause regular ocean waves.