How Does the Moon Affect the Tides?

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How or why does the phase of the moon affect the tides?                                                                                                                                          Dave Walter                                                                                                                                                                                                                      Klamath Falls

The tides are the natural rising & falling of major bodies of water present on our planet. For example, the oceans & large lakes. Tides are caused by the gravitational relationship between both the Earth & the moon. The moon’s gravity pulls on the Earth causing the water to swell in the direction of the moon.

Because our earth rotates, and the moon is also orbiting, we have two high tides a day and two low tides. Imagine you are looking at the Earth from the North pole. To the west is the moon. High tide would be present on both the west side of the earth and also the east side. This is because the moon is gravitationally pulling water towards it, but on the east side an equal and opposite force is pulling water in the opposite direction. This equal and opposite force is known as the earth’s centrifugal force. Both the west and east side of the earth is where the high tides would be. To the north and the south is where water is receding & the low tides would be because water is being drawn towards the high tides.

Dave also mentioned that when Hurricane Sandy made landfall it was high tide because we had a full moon. Not only do we have a daily high and low tide cycle, but a month high and low tide cycle. When we have a full moon, the high tides are at their highest. Hurricane Sandy made landfall both during the daily high tide, and also the astronomically high tide of the month. When a hurricane makes landfall the biggest threat is storm surge–the rising of water from an area of low pressure and onshore wind flow. Combining the storm surge (rising of water from hurricane) with the high tide, gives you the storm tide. This is the reason Hurricane Sandy was so devastating. The high tide added at least 1-2′ of water in some locations.