Geology of Puʻuhonua o Hōnaunau National Historical Park
Geology of Pu‘uhonua o Hōnaunau National Historical Park
Pu‘uhonua o Hōnaunau National Historical Park is located on the Big Island of Hawai‘i, also known as Kona Island. The Hawaiian Islands are an archipelago, or group of islands, positioned in the North Pacific Ocean, roughly 2,400 miles (3,862 km) off the coast of California. They are the visible tops of submarine volcanic mountains that extend to the seafloor. These islands formed as remnants from hotspot volcanism, in which the Pacific tectonic plate migrated over a relatively stationary thermal plume in the underlying mantle, allowing for magmatic build up to acquire over time and form the volcanoes of Hawai’i.
Kona Island, the largest and southernmost island of Hawaii, is home to three active volcanoes: Kīlauea, Mauna Loa, and Hualālai. These volcanoes have supplied the land mass of the island, in which overlying basalt flows have cooled atop one another throughout Hawaii’s eruptive history. Pu‘uhonua o Hōnaunau National Historical Park is situated on the east coast of Kona, which spans 10,432 km2 (4,028 mi2) in its entirety. This Park covers 169.9 ha (419.8 ac) of land along the shoreline, out of which 73.57 ha (181.80 ac) is designated as federal land. The seaward-sloping land of this Park sits at the base of Mauna Loa and is bordered by a low-lying bench of relatively young pahoehoe lava flows near Pu’uhonua (“Place of Refuge”) Point and Hōnaunau Bay, an adjacent marine resource area. To the north lies Keone’ele Cove, a small artificially nourished beach with a nearshore volcanic platform used by sea turtles as a haven for sunbathing. This cove is also an ancient royal canoe landing area and is now managed by National Park Service staff under an agreement with the State of Hawai’i.
Along the coastline of the Park lies pockets of sandy beaches, rocky areas, and basalt boulders. The relief, or elevation change, within the Park is generally about 30 meters (100 feet) aside from the Keanae‘e Pali (cliffs) along the coast, which dramatically rise to about 37 meters (120 feet) from sea level. There are roughly three major lava flows that run through the Park: a 750-1,500 year-old flow, a 3,000-5,000 year-old flow, and a 1,500-3,000 year-old flow as seen in the image below.
Pu‘uhonua o Hōnaunau National Historical Park is known for its rich cultural history, dating back to the death of King Kamehameha I in 1819. Pu‘uhonua, meaning “place of refuge”, was the only option of survival for defeated Hawaiian warriors and those who were sentenced to death for violating the kapu (laws of conduct). This Park is also an old Hawaiian religious site that has truly stood the test of time. Many features revealing the daily life of ancient Hawaiians can be found on the sacred ground within the Park; including abandoned heiau (temples), Ki‘i, (carved wooden images), Hale o Keawe (memorial houses of past chiefs), agricultural features, church foundations, and animal pens. Pu‘uhonua o Hōnaunau National Historical Park and the adjacent Keone‘ele Cove provide habitats for endangered species ranging from birds to turtles to seals, and contains over 157 vascular plant species. This site became a National Historic Park on July 26, 1955, to benefit and inspire people, preserve cultural and historical resources, and protect the natural ecosystem in the area.
The USGS has worked in cooperation with the National Park Service to create a report outlining the geology and coastal landforms of Pu‘uhonua o Hōnaunau National Historical Park, with the intent to educate others of natural resource sensitivity and fundamental environmental awareness. While the primary resource management emphasis is centered around the preservation of the historical setting within the Park, there are several geologic and natural resource concerns that also require consistent management. Hawaii is the only state in the United States that is subject to volcanism, tsunamis, earthquakes, and hurricanes. The landscapes of each island are shaped by wind and water erosion, rising sea level, seasonal high tides.
Groundwater recharge and accessibility to fresh water on Kona Island are dependent on the age and geologic structure of a given area. Typically, freshwater in Hawaii is sourced from unconfined aquifers or vertically extensive freshwater bodies that float atop of saline groundwater. The best developed aquifers are located in the volcanic rocks formed during the main shield building process of Hawaii. The volcanic rock in other areas of the island are highly variable in geologic makeup and permeability, leaving limited reliable freshwater sources on the island. Saltwater intrusion, or encroachment of saltwater from the ocean into upstream or near land freshwater bodies, tends to be a concern at Pu‘uhonua o Hōnaunau National Historical Park due to its proximity to the ocean. The Park is also located on the leeward side of the island where the trade winds are blocked by Mauna Kea and Mauna Loa, resulting in less precipitation in lower elevations on the east coast. Precipitation that occurs at the summits of the volcanoes do carry about 102 cm (40 inches) downslope per year, but the lava flows that make up the island have a high permeability and the absorption of water tends to keep aquifer retention low. Since the island is made of steep volcanic slopes, precipitation events are marked by quickly rising water levels followed by high runoff rates due to the lack of channel storage. This could further cause flash flooding and increased erosion. A greater understanding of these hydrogeologic processes allow scientists to manage water resources effectively, predict and prepare for hydrologic events, and make recommendations for watershed issues, habitat protection, and ecological restoration. Currently, USGS scientists are calculating groundwater recharge by utilizing geophysical techniques, such as thermal infrared scanning and low-level aeromagnetic surveys. The data collected allows them to model underground structures and the relation between saline and freshwater interaction around the island. In addition, the USGS Water Resources Division-Hawaii District operates a network of monitoring devices to collect information on precipitation, salinity, stream discharge, and evapotranspiration.