Physiolography of the Hawaiian Islands

Each of the eight principal Hawaiian Islands extending from Kauai on the northwestern end of the chain to Hawaii at the southeastern extremity represents the top of a great basaltic shield volcano that rises 4575 m above the ocean floor. The ages of the islands quite consistently decrease toward the southeast. Kauai is judged to be about 5.3 million years old, whereas Hawaii is less than 750,000 years in age. The ravages of time have had serious effects on the once domelike older volcanoes, so that the traditional shield shape is lost in a fretwork of peaks, ridges, palis, valleys, and plains. Age is not the only determinant of the degree of dissection by running water, waves, and chemical weathering. Another very important factor is the exposure of the particular side of island to excessive rainfall and mercilous trade-wind wave attack. The windward and high lee slopes receive 60 cm or more of rain annually, whereas the lower leeward slopes and coastal areas may receive 4 cm or less annually.