Hawaiian volcanic rock aquifers

Volcanic-rock aquifers extend throughout the eight major Hawaiian Islands and are the most important sources of potable ground water. Sedimentary deposits overlie the volcanic-rock aquifers in some areas. Because the island of Hawaii has not been extensively eroded, sedimentary deposits there are not widespread. The isthmus of Maui contains sedimentary deposits overlying the volcanic-rock aquifers. Sedimentary deposits exist in some coastal areas on the islands of Kahoolawe, Lanai, and Molokai. On Oahu and Kauai, sedimentary deposits act as caprock to the underlying volcanic-rock aquifers. Sedimentary deposits on Niihau occur mainly in the southeastern and northwestern parts of the island.