kauai (kaua'i in hawaiian) is the second oldest (after ni'ihau) and fourth largest of the main hawaiian islands, in the united states. known also as the "garden isle", kaua'i lies 73 miles (117 kilometers) across the kauai channel, northwest of honolulu on oahu. it is of volcanic origin. the highest point on the island is kawaikini. it is located above sea level. the wettest spot on earth, with average rainfall of a year, is just east of mount waialeale. the high yearly rainfall has eroded deep valleys and canyons in the central mountain. the waterfalls that have been created by erosion in canyons are now popular tourist spots.