Most Polynesian archipelagoes have a volcanic ‘hot spot’ origin and, due to tectonic plate movement, islands increase in age as one progresses further from the hot spot of volcanic activity. The Hawaiian Islands illustrate this geological age progression, and associated opportunities for crop production.
The geographically older westerly islands (Kauai, O‘ahu, Molokai and west Maui) are more heavily weathered, with permanent stream flow and alluvium valleys, on which irrigation could be developed. The agricultural emphasis was on taro irrigation, with shifting cultivation and other forms of dryland gardening providing a secondary role. In the geologically younger islands to the east (east Maui and Hawai‘i), irrigation was only a minor contributor to subsistence production and highly labor-intensive, short-fallow dryland field systems predominated.