Thermal infrared weathering trajectories in Hawaiian basalts: results from airborne, field and laboratory observations

Abstract

Basalts are ubiquitous in the inner solar system. They are known to occur on the Moon, some asteroids (particularly Vesta), Mars and seventy percent of the surface of the Earth. A small fraction of Earth's basalts are exposed subaerially on high oceanic volcanoes including Hawaii, the Canaries and the Galapagos. Remote sensing studies of these volcanoes must include an understanding of the effect of weathering on their surface physical and chemical properties. Such an understanding is, to some extent, even relevant to studies of basalts on Mars that may have been weathered by processes analogous to those that occur on high oceanic islands. The range of weathering zones and ages of basaltic lava flows on the Island of Hawaii make that locale ideal for the study of basaltic weathering. This was recognized by Farr and Adams [1984] and Kahle et al. [1988] who conducted field, laboratory and remote sensing studies of basaltic lava flows of Mauna Loa volcano. These studies found systematic relationships among physical properties, spectral properties, ages and environmental conditions of individual flows. Since that pioneering work, substantial progress in the technology of remote sensing and field spectral measurement has occurred. In this thesis I revisit the study area of Kahle, et al. [1988], and use these new methods to confirm the earlier studies and to extend them. I obtained both field spectroscopic and remote sensing data of similar quality to those obtainable in the laboratory, allowing the effects of disturbance by sampling to be controlled, and to assess the variability of spectral properties within flows. The spectral work is supported by sample analysis of the elemental properties of samples collected from the sites to understand the controls on the observed spectral behavior. I confirm the results of the earlier studies, and show that no new insights are available from my new data; however, the confidence in the earlier results is substantially improved by my more comprehensive and controlled study.