Airborne electromagnetics - Providing new perspectives on geomorphic process and landscape development in regolith-dominated terrains

In regolith-dominated terrains, the nature of contemporary processes and th e surface distribution of regolith materials may be a poor guide to the cha racter and history pf regolith materials at depth. The nature of regolith m aterials at depth is often critical to unravelling the development of a lan dscape. Conventional mapping aids such as air photos, multispectral remote sensing and airborne radiometrics are not wholly adequate in this context, as they penetrate limited depths (<0.4 m). Airborne electromagnetics (AEM) on the other hand, has the potential to map regolith materials to considera ble depths (>100 m). The application of AEM to regolith mapping and its potential as a tool in g eomorphology are illustrated by reference to an AEM survey flown at Lawlers in the Yilgarn Craton of Western Australia. At Lawlers, AEM identifies a p alaeochannel that has no surface expression. It cannot be seen in images of the Landsat, airborne radiometric or airborne magnetic data. The dispositi on of this channel in the landscape, and in particular its association with ferruginous materials forming breakaways, suggest that inversion of relief has been a significant factor in the evolution of the Lawlers landscape. The AEM data at Lawlers have also been used to map the weathering front. Th e topography of the weathering front not only reflects the movement of wate r through the landscape in a general sense, but also reflects the influence of lithology and structure. Different lithologies are clearly weathering t o different depths. Information on the nature of the weathering front is po tentially an important constraint on models of groundwater flow, and by ass ociation, models of solute dispersion. (C) 1999 Elsevier Science Ltd. All r ights reserved.