Geology and Soils

General Soil Profiles and their Defining Characteristics
Hakalau Soil Map 520x380

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.

Soil Types Within Hakalau Forest and Key Characteristics

PUCModerately rapidSlowSlight
LADModerately rapidMediumModerate


Pu‘u ‘O‘o silt loam, 6-12 percent slopes (PUC):

Located on uplands of the windward side of Mauna Kea between 5,000 - 6,500 ft, soils in the Pu‘u ‘O‘o series are gently sloping to moderately steep. The surface layer is dark reddish-brown and very dark gray silt loam. This layer is approximately 6 in thick and can be strongly acid (pH 5.1 - 5.5) to very strongly acid (pH 4.5 - 5.0). The subsoil, which is about 21 in thick, is very dark brown to dark reddish-brown silty clay loam. Material underlying the subsoil is dark yellowish-brown and darkbrown sandy clay loam. These layers range from strongly acid to extremely acid (pH below 4.5). 

Laumai‘a silt loam, 6-20 percent slopes (LAD):

The Laumai‘a series are undulating soils located on high elevations above 5,500 ft of the windward side of Mauna Kea and are gently sloping to moderately steep. The surface of the Laumai‘a silt loam is a 12 in thick layer of very dark brown and dark-brown silt loam that is exceptionally stony in certain areas. The subsoil is roughly double in thickness and is very dark grayish-brown and dark brown silt loam. The degree of acidity ranges from medium acid (pH 5.6 - 6.0) at the surface layer to strongly acid at the subsoil. 

Hanipoe very stony loam, 12-20 percent slopes (HCD):

The Hanipoe series is found from 5,000 - 6,500 ft in elevation. Hanipoe very stony loam is composed of a 20-30 in layer over fragmental ‘a‘ā lava.

Pi‘ihonua silty clay loam, 6-20 percent slopes (PND):

The Pi‘ihonua series, located from 4,500 - 6,500 ft on the windward side of Mauna Kea, consists of well-drained silty clay loams that have a banded appearance. The surface layer is about 6 in thick and comprised of very dark brown silty clay loam that is extremely stony in certain areas. The subsoil is dark-brown to dark-red silty clay loam about 44 in thick, while a weakly cemented layer of volcanic ash occurs at a depth of 17-25 in. Acidity varies between very strongly acid to extremely acid.

Pi‘ihonua extremely stony silty clay loam, 6-20 percent slopes (POD): 

In addition to the characteristics of Pi‘ihonua silty clay loam, 6-20 percent slopes, stones cover 3-15 percent of the surface in this soil.  

Facts About Geology and Soils

Hawai‘i Island is the largest and youngest island in the Hawaiian chain and encompasses a total land area of 4,028.2 mi2. The landmass was formed when fivevolcanoes of varying ages (Kohala, Mauna Kea, Hualālai, Mauna Loa, and Kīlauea) joined together. 

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. The elevation of Mauna Kea is13,796 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.