Rock varnish on Hualalai and Mauna Kea Volcanoes, Hawai'i

Tropical rock varnishes found on Hualalai and Mauna Kea Volcanoes, Hawai'i, vary systematically with time and environment. Radiocarbon dating of encapsulated organic matter, (K⁺ + Ca²⁺)/Ti⁴⁺ ratios, and Zn, Cu, and Ni trace element concentrations in rock varnish are consistent with lava flow ages established by K-Ar and ¹⁴C dating, where samples are collected from arid microsites well away from the soil surface. However, inaccurate ages are obtained from rock varnish in subsurface locations and from sites with abundant lichens, cyanobacteria, and fungi that chemically erode varnish. Laboratory experiments on Hawaiian rock varnishes indicate that K and Ca are preferentially leached relative to Ti over time and at higher temperatures. -from Authors