Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Prevailing trade winds are weak along the Kona coast because the winds are blocked by Mauna Loa
and Hualālai (Juvik and Juvik 1998). Mean annual wind speeds in the area are less than 12.3 mph
(HECO 2004).
3.2 Geology and Soils
The Hawaiian Islands were formed by a series of volcanic eruptions that occurred at various hotspots
beneath the Earth’s crust. As the tectonic plate slowly drifted, magma welled up from fixed spots
creating a linear chain of islands. Hawai‘i Island is the largest and youngest island in the Hawaiian
chain and encompasses a total land area of 4,028.2 mi 2 . The landmass was formed when five
volcanoes of varying ages (Kohala, Mauna Kea, Hualālai, Mauna Loa, and Kīlauea) joined together
(Juvik and Juvik 1998).
Dated at 430,000 years, the extinct Kohala volcano is the oldest on Hawai‘i Island. Found on the
northeastern portion of the island, this volcano is deeply eroded on the windward side. Mauna Kea is
a dormant, postshield volcano with the oldest lavas estimated to be roughly 250,000 years old and the
most recent approximately 4,500 years old (Juvik and Juvik 1998). The elevation of Mauna Kea is
13,796 ft; however, when measured from the submarine base to its peak, Mauna Kea is considered
the world’s tallest mountain, with a height of 33,480 ft (HDBEDT 2007). Hualālai is an active,
postshield volcano on the western side of Hawai‘i Island. Although Hualālai last erupted in 1801,
alkalic basalt eruptions generally occur every few hundred years so its core is still active (Juvik and
Juvik 1998). Mauna Loa is an active shield volcano with an elevation of 13,679 ft (HDBEDT 2007).
Embedded in the eastern flanks of Mauna Loa is Kīlauea, the youngest and most active of the
volcano on the Island of Hawai‘i. Since January 1983, Kīlauea has continuously erupted, discharging
lava and occasionally ash deposits (Juvik and Juvik 1998).
As the basaltic lavas and volcanic ash from the volcanoes weathered and decomposed, various soil
types developed throughout the island (Juvik and Juvik 1998). Soils on the Island of Hawai‘i were
classified by the U.S. Department of Agriculture (USDA) Soil Conservation Service (Foote et al.
1972). Soil types are mapped in Figures 3-1 and 3-2. Key characteristic of the soils found within the
units are listed in Tables 3-2 and 3-3.
3.2.1 Hakalau Forest Unit Geology and Soils
The majority of the unit is covered in Laupāhoehoe Volcanics from a Mauna Kea lava flow ranging
between 11,000-64,000 years old. Laupāhoehoe Volcanics in the Maulua Tract of the Refuge are
younger, primarily dated between 5,000-11,000 years old. Smaller areas of Hāmākua Volcanic from
the Pleistocene epoch (dated between 64,000 and 300,000 years old) occur in the southwestern and
northwestern corners of HFU.
All of the soil series present in the HFU were formed from volcanic ash. In the upper elevations of
the unit above 5,000 ft, the soil is classified as well-drained silt loams, while lower portions of the
Refuge are composed of silty clay loams. The USDA Soil Conservation Service has identified the
following soil types:
3-4 Chapter 3. Physical Environment