Ahupua'a 'o Kahana EarthCache
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Found in Ahupua`a `o Kahana State Park on the windward side of O'ahu. You'll need either a kayak/canoe for easiest access or be in really fit swimming shape to log this one.
Cultural Notes:
Ahupua`a `o Kahana State Park is on the windward side of O`ahu and it comprises the the entire ahupua`a of Kahana. For those of you not familiar with traditional land divisions, an ahupua`a is an ancient Hawaiian division of land, usually a wedge shape, that begins in the mountains and runs toward the sea. "Hawaiians used these land divisions to provide everything they needed to survive-from forest birds, wild pigs, and trees of the upland forests to the lower-lying taro lo`i, down to the ocean, the primary source of food and transportation" (Jaworowski, 2001).
"Kahana is unique in being the only remaining ahupua`a in the major Hawaiian islands owned by one owner, and the only one in the whole State owned by the government. In recognition of this rarity, the Kahana Valley State Park was renamed the Ahupua`a `o Kahana State Park in November 2000. At 5,228.7 acres, Kahana is the second-largest state park in the state park system. Like all land in Hawaii, it was originally owned by the King. It is estimated that the ahupua`a may have had between 600 and 1,000 people before Western contact. After the dying off of great numbers of the Hawaii people due to Western diseases, at the time of the Great Mahele, there were an estimated 200 people in the ahupua`a" (Jaworowski, 2001).
Geology and Hydrology Notes:
The Kahana Valley and Kahana Stream are found in the heavily eroded Ko'olau basaltic shield volcano remnant. "The Ko'olau volcano was primarily composed of a series of thin-bedded, overlapping gently-sloping basaltic lava flows. These flows were fed by magma pouring out of fissures in the volcano. When molten rock solidifies the narrow cracks under pressure, rock is created which is much denser and much less permeable than the surrounding porous lava flows" (City/County of Honolulu [CCH], 2004). This dense rock structure, usually formed vertically, is known as a volcanic dike.
"The volcanic dikes control most high-level water in Windward O'ahu. The Ko'olau Loa dikes underlie the upper mountainous portions of the watershed and serve as barriers [aquicludes] that prevent groundwater from easily moving from the upper part of the watershed to the coastal areas" (CCH, 2004).
"Dikes and dike complexes divide Ko'olau Loa groundwater sources into upper mountain and lower coastal areas. The water stored behind the dikes is referred to as high-level water as the dikes prevent the water from coming in contact with saltwater. The high-level water recharges the basal aquifers, provides stream flow and provides high quality potable water" (CCH, 2004) you'll find at this Earthcache.
"Basal groundwater is a groundwater body that overlies seawater composition. Freshwater floats on top of the salt water within the basalt formation owing to freshwater being less dense. The lower part of Ko'olau Loa" where this cache is located, "contains the basal waters" (CCH, 2004).
The Kahana aquifer is mostly confined by high-level dikes, but there are smaller dike-basal aquifers in the lower portion of the valley. Much of the high-level ground water seeps into the streams in Kahana Valley, primarily in those areas where the dikes have been infringed due to erosion (CCH, 2004).
References:
City and County of Honolulu, Board of Water Supply. (2004). Koolau Loa Watershed Management Plan, Chapter 2 - Ko'olau Loa watershed profile. Retrieved January 14, 2007, from http://www.boardofwatersupply.com/files/KL_WMP_06_Chapt2_WatershedProfile.pdf
Jaworowski, S. (2001). Kahana: What was, what is, what can be. Legislative Reference Bureau, Report No. 5. Honolulu, Hawaii. Retrieved January 14, 2007, from http://www.hawaii.gov/lrb/rpts01/kahana.pdf
Resources:
O'ahu Regional Aquifer System graphics (USGS) - http://capp.water.usgs.gov/gwa/ch_n/N-HIOahu1.html
Oblique Aerial view of Kahana Bay and Valley - http://www.soest.hawaii.edu/coasts/data/oahu/pictures/oblique_photos/showpic.php?gal=Windward&pic=028_Kahana_Bay.jpg
To claim and log this Earthcache you must include a picture of you at the cache location with the Ko'olau pali (cliffs) in the background.
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