Tidal waves are caused by the gravitational pull of the sun and moon on the Earth. The moon's gravitational pull has a greater influence on Earth because it is closer. The moon creates a bulge in the ocean on the side of Earth closest to it.
A bulge also develops on the side of Earth opposite of the moon. Since Earth makes a complete rotation every 24 hours, one part of Earth is under a bulge at any given time, experiencing high tide every 6 1/2 hours. Semidiurnal tides are two high tides and two low tides each day. A diurnal tide is one low tide and one high tide per day. During full moons and new moons, the sun, moon and Earth are lined up, and Earth experiences higher high tides and lower low tides. Called spring tides and neap tides, these occur twice a month.
Shore-based water-level gauges track tidal movements. These networks track tidal movements of certain locations to help determine future levels of low and high tides and when they will occur. The highest tidal range in the world happens in the Bay of Fundy in Nova Scotia, Canada. Ranging from 11 feet to 53 feet, these tides have created enormous cliffs through erosion.