Journal
EARTH SURFACE PROCESSES AND LANDFORMS
Volume 39, Issue 3, Pages 381-398Publisher
WILEY
DOI: 10.1002/esp.3505
Keywords
basalt; base-level; chemical weathering; Hawaii; vadose zone; water balance
Funding
- Birgit and Helmuth Hertz's Foundation, through the Royal Physiographic Society in Lund
- Wenner Gren Foundation in Stockholm
- Terman Fellowship
- NSF [NSF-DEB-0918234, NSF-DEB-1020791]
- Gordon and Betty Moore Foundation
- Direct For Biological Sciences
- Division Of Environmental Biology [1020791] Funding Source: National Science Foundation
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Using field observations and geochemical and digital terrain analyses, we describe the structure and thickness of the regolith across a climosequence on the island of Hawaii to gain insight into the relative roles of precipitation and the near-surface hydrologic structure in determining weathering patterns. In the wet portion of the climosequence, where the long-term water balance is positive, the regolith thickness reaches an observed maximum of similar to 40m and appears limited by the geomorphic base-level of the landscape. However, even within this thick regolith, distinct units of varying weathering intensity occur; the vertical ordering of which largely reflects differences in the initial permeability structure of the basalt flows rather than a systematic decrease in weathering intensity downwards from the ground surface. In the dry portion of the climosequence, where the long-term water balance is negative, the regolith thickness is confined to similar to 1m, is highly dependent on the inferred permeability structure of the basalt flows, and is independent of geomorphic base-level. Weathering intensity also varies according to permeability structure and decreases in this thin regolith with distance beneath the ground surface. The abrupt change in regolith depth and character that coincides with the transition from net-positive to net-negative long-term water balance implies that small changes in precipitation rates around a neutral water balance result in large changes in the distribution and depth of weathering. Together our observations indicate that the distribution and depth of weathering in basalts (and probably other lithologies) might be best understood by considering how precipitation interacts with the complicated near-surface permeability structure over regolith-forming timescales to weather rock in the vadose zone. Copyright (c) 2013 John Wiley & Sons, Ltd.
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