Geologically, the top soil layers of the islands of Hawaii are young. Because it takes soil ages to become well developed, the islands have sparse amounts of the best soil types for growing. According to Encarta Encyclopedia, less than 10 percent of Hawaii's land area is covered by well-developed soils.
Climate plays a significant role in the end product of soil development. Average annual temperature and rainfall vary widely on the Hawaiian Islands in direct relation to the altitude. Higher elevations experience cooler average temperatures and lesser amounts of annual precipitation. The best developed soils are on the lower lands of the islands of Hawaii, Kauai, Maui, and Oahu due to erosion and leaching of minerals to lower elevations. Farmers have used these more fertile areas to produce sugar cane and pineapple crops.
Many of Hawaii's soil types develop in volcanic ash deposited over pahoehoe or aa lava. Pahoehoe is a smooth basaltic rock formed from free-flowing lava, as opposed to aa volcanic rock which has rougher surfaces and spiky features. A soil survey of the islands completed by the USDA shows that which type of lava rock underlies the surface soils determines to a great extent the prevalent soil types. Generally, soils formed over pahoehoe are more fertile.
At Pulehu on the island of Maui, the USDA has recorded very stony clay loam. Stony silty clay is present at Hanalei, in Kaua'i County on the island of Kauai and at Waialua (North Shore) and Waikane on the island of Oahu.
According to the Soil Science Society of America, each state and territory of the United States has a representative soil, like a state tree or state bird. The United States Department of Agriculture Natural Resources Conservation Service lists the hilo series as the official state soil of Hawaii. The USDA describes the hilo soil series as developing from multiple layers of volcanic ash intermixed with slight amounts of dust from central Asian deserts. In a sample hilo soil profile, the surface layer and subsoil layers consists of silty clay loam, with a color differentiation marking the layers. Hilo soils exist on the big island of Hawaii and the island of Maui.
Silty Clay and Silty Clay Loam
Silty clay and silty clay loam soil types are present on Oahu Island around Ewa, west of Honolulu; at Haleiwa on the North Shore; at Kaneohe in Honolulu County, on the southeastern coast of Oahu; at Paumalu, the original Hawaiian name for what is now known as Sunset Beach on the North Shore of Oahu Island; and at Wahiawa, in the valley between the two volcanic mountains of Oahu. Silty clay and silty clay loam soils also occur at Lahaina, on the west coast of the island of Maui; at Manana, an islet lying out from the eastern end of Oahu Island; and at Molokai, known as the Friendly Island, located between Oahu and Maui islands.
- "Science 101 Geology;" Mark A. S. McMenamin; 2007
- U.S. Department of Agriculture: Volcanoes National Park Soil Survey
- "Encarta Encyclopedia;" Microsoft; 2004
- Photo Credit Summer Hawaiian Hillside image by LittleDrummerBoy from Fotolia.com