The spring tides occur twice a month, once after the new moon phase, and once after the full moon phase. When the spring tide occurs after the new moon phase, the sun, moon, and earth are aligned in a straight line, with the moon being between the sun and the earth. When the spring tide occurs after the full moon phase, the sun, earth, and moon, are again aligned in a straight line, but this time it is the Earth that is between the sun and the moon.
These tides are the ones that cause the greatest difference between the high tide and the low tide. The high tide is the highest of the tides, thus it is abnormally high, while the low one is the lowest of the tides, thus abnormally low. This results in a very big difference between the high tide and the low tide. This happens because the gravitational pull from the moon and sun is slightly greater when they are aligned in this manner, thus they pull the water surfaces further up.
