When the tide is low, it's said to be minus tide. This means that the water level is lower than normal. The average low tide is about 1 foot (30 cm) below the mean sea level. But during a minus tide, the water can drop more than 3 feet (90 cm).
Minus tides are caused by a combination of the moon's position and its phase. The moon orbits Earth every 27.3 days. And as it does, its position changes relative to the sun. There are two main positions that create extreme tides:
1) When the moon is directly between the Earth and sun (new moon).
2) When the Earth, moon, and sun are lined up with the Earth in between (full moon).
The first position creates high tides because the gravity from both celestial bodies pulls on all of the oceans at once. The second position also causes high tides, but not as extreme as during a new moon because only part of the ocean is being pulled by both gravitational forces—the rest is being pushed away from them.
A third factor that determines how extreme a tide will be is whether or not there's an obstacle in its way—like a continent. If there's land in the way of where tidal waves would normally go, they'll build up and crash against it with more force than if there was nothing there blocking their path