The island of Maui is the second largest in the Hawaiian chain and is referred to as the "valley isle" because of its huge central valley created between the older West Maui Mountains and the newer Mount Haleakala which forms the eastern coasts. The West Maui mountains have been extinct for the last million years but Haleakala is considered dormant and will someday in all likelihood show signs of volcanic activity again although, the last brief eruptions were back in the 1790's. Maui County is actually made of four distinct islands which share the same enormous underwater mountain foundation. These islands are Maui, Molokai, Lanai and Kahoolawe in addition to a famous and prominent off-shore crater-head well-known for its snorkeling called Molokini. The West Maui Mountains raise to a height of about 5000' and Haleakala raises close to 2 miles above sea level to a height above 10,000'. The top of Haleakala is famous for its immense crater which descends 3000' and is about 21 miles in circumference. Maui is known for its variation of rainfall and as such contains many microclimates within its short 48 mile length. Maui's leeward coastlines have white sand beaches and relatively little rainfall where as Maui's windward coasts can have rainfall averages in places over 100 inches and are covered in lush dense tropical rainforests.