Volcano Watch — Kapaho Cone, an ash and tuff cone

The superintendent for the parks maintenance division of the Hawaii County Parks and Recreation Department recently called the U.S. Geological Survey's Hawaiian Volcano Observatory to inquire about a possible source of cinder/ash mixture similar to that found at Kapoho Cone.

The county lost its access to this resource and wanted to find an alternate site. The cinder/ash mixture found at Kapoho Cone is ideal for baseball infields because there is sufficient cinder in it to allow water to drain and enough ash to make it cohesive and allow compaction.

With the numerous volcanic cones on the island, one would think that this question would be relatively easy to answer, but Kapoho Cone is unique. It is an ash and tuff cone.

Unlike cinder or spatter cones that form around eruptive vents from lava fountaining, ash and tuff cones are the product of the explosive contact between magma and water at a shallow depth. This hydromagmatic activity results in a lower, broader cone with abundant sand- and silt-sized particles. If the particles are not cemented together, it is an ash cone. Weathering and oxidation often turn the gray ash particles to a light-brown reddish color, cementing them to form a rock called tuff. The resulting edifice is a tuff cone. Because of the explosive origin of the deposits, large angular blocks are also commonly found in them.

Based upon the geologic stratigraphy of the area, the eruption that formed Kapoho Cone probably took place less than 400 years ago. Green Lake, a depression within Kapoho Cone, is thought to be one of four vents that erupted explosively to produce the ash.

During the early stages of the 1960 Kapoho eruption that formed Pu'u Laimana to the north of Kapoho Cone, seawater entered the magma conduit system, and wet, black ash containing salt erupted for three days. Subsequent cinder and spatter deposits have covered this ash layer, but small steam explosions continued sporadically to the end of the eruption.

The low elevation of the Kapoho region, with the resulting shallow depth to the water table, is the reason for the explosiveness of the eruptions in that area. More famous tuff cones in Hawai'i are also found at lower elevations. These include Diamond Head, Koko Head, Punchbowl, and Salt Lake tuff cones on O'ahu.

Baseball fields on the Big Island will now have to depend on man to prepare the proper mixture of ash and cinder, which nature once did perfectly at Kapoho Cone, for their base paths.