Diversity - Geology

Maui is the second largest of the Hawaiian Islands and it is made up of two volcanoes, West Maui and Haleakala (East Maui), which are connected by a broad flat plain called the isthmus. The elevation of West Maui volcano is 1,764 m above mean sea level (5,788 ft), while that of Haleakala is 3,055 m (10,023 ft). The volcanic rocks are primarily basalt and basaltic andesite, including some andesites and trachytes, which are the parent rocks associated with soils such as Mollisols, Oxisols, and Ultisols. The major portion of the domes is the primitive olivine basalt but the later eruptions include andesites and trachytes (Stearns and Macdonald, 1942).

Figure 5. West Maui and East Maui with weather stations.

West Maui is thought to have erupted above sea level in the middle or late Tertiary period with later eruptions extending into the early and late Pleistocene period. Haleakala or East Maui, on the other hand, is thought to have erupted above sea level in the Pliocene period, and the later eruptions range from the early and middle Pliestocene period to the late Pleistocene and Recent periods. In addition to the lava flows, pyroclastic eruptions including volcanic ash are associated with the Haleakala eruption (Stearns and Macdonald, 1942) and with volcanic ash soils classified as Andisols.

Haleakala volcano, therefore, is geologically much younger than the West Maui volcano. Basalt and basaltic andesite are the dominant parent rocks which form the parent materials of many of the soils. In addition, pyroclastic eruptions, including volcanic ash, and cinder cones of East Maui volcano are the parent materials of soils classified as Andisols.

Figure 6. Basaltic-andesitic rocks (>20-cm depth) form soils such as Molllisols, Oxisols, and Ultisols.


Figure 7. Layers of pyroclastic and volcanic ash parent materials form Andisols.

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