Introduction: Overview of concepts, definitions, and principles of soil mound studies

Abstract

This volume grew out of a symposium titled: "The origin of Mima mounds and similar micro-relief features: Multidisciplinary perspectives," and an associated similarly themed fi eld trip, both held at the Geological Society of America Annual Meetings, Houston, Texas, 4-9 October 2008. Five of the eight papers in that symposium were expanded for inclusion in this volume; with one nonsymposium paper added later (Johnson and Johnson, Chapter 6). The volume was invited and encouraged by the editors of GSA Special Papers to be one of their series. In regard to soil mounds, the symposium was timely for several reasons. The fi rst was, among the innumerable theories on how mounds form, evidence has gradually accumulated which confi rms that burrowing animals are involved. Involvements would seem to include (1) animals initiating the mounds themselves, where they begin as "activity centers" for basic living purposes (denning, reproduction, food storage, safety, etc.), which are actively bioturbated; (2) where landscape microhighs created by some physical or biological process, or both (e.g., coppicing), become occupied by animals for "activity centers," then augmented through bioturbation to create "hybrid mounds"; or (3) occupy soil-fi lled joints and fi ssures in otherwise thin soil or eroded bedrock areas. 1 In any of these three conditions we are concerned with the question: Would activity centers evolve into mounds, and perhaps persist wherever the centers confer living-survival-reproductive advantages to the animals that inhabit them? Since we examine mounds after they form, how can we tell, beyond theorizing, what the initial conditions were that led to mound formation? A purpose of the symposium, and this volume, was to revisit and examine these and other soil mound issues and questions, especially the role of life in landscape evolution. A second reason is the recent availabilities of useful analytical tools, such as LIDAR (light detection and ranging) and Google Earth technologies, allow new and different light to be shed on soil mound matters. In fact, they are revolutionizing studies of mounded landscapes. Third, bioturbation-and biomantle-related ideas and formulations on pedogenesis have appeared that are spawning different genetic understandings on how soils form and landscapes evolve

Ecohydrology: Processes and Implications for Rangelands

“…The origins of the mima mounds in North America are no less controversial, but in this case small mammals (gophers) appear to be the primary drivers for the accumulation of materials (Whitford and Kay 1999;Jackson et al 2003;Horwath and Johnson 2006;Johnson and Horwath-Burnham 2012). Whether or not that proves to be the sole explanation, these features also accumulate materials and alter the ecohydrology of the landscape.…”

Preservation of thin tephra

“…The available evidence suggests that pocket gophers, despite individual lifespans of only 2-3 years (Johnson and Horwath Burnham 2012), have almost completely reworked 20-40 mm thick layers of W tephra in alpine meadow sites in 500 years or less. This is in accord with the observation of Andersen and MacMahon (1985) that gopher activities had covered up to 2% of the ground surface with pre-Mount St Helens 1980 soil in the first 4 months after the 1980 eruption and with those of Kyoo et al (2005) where soil turnover in the upper 50 cm by gophers occurs in only 40-100 years on California hillslopes.…”

Critiques of the seismic hypothesis and the vegetation stabilization hypothesis for the formation of Mima mounds along the western coast of the U.S.

“…Similarly, the geomorphic evidence argues against the hypothesis that the mounds could have formed through fluvial erosion: the moundfields do not have extensive and well-developed drainage systems that could have removed a large volume of sediment from between the mounds and transported it long distances. We also note that, in the Central Valley moundfields, low bridges of soil connecting mounds create closed depressions in many of the intermound areas (Nikiforoff, 1941), a clear impediment to flowing water (Johnson and Horwath Burnham, 2012). Thus, whereas there is unambiguous evidence for gophers pushing soil toward Mima mounds and up them (Cox and Allen, 1987), there is none demonstrating that sediment transport by wind or flowing water is an important process.…”

“…Similarly, in the Shasta Valley of northern California (Fig. 1), a new moundfield has been forming on a dirt road that fell into disuse in 1965 (Johnson and Horwath Burnham, 2012). The only earthquake of note in the region since then was an M w 5.1, in 1978, with an epicenter~70 km away from the mound site (USGS, 2016).…”

“…The type locality for Mima mounds is the Mima Prairie in Washington State (Fig. 1), and similar mounds can be found along the western coast of the U.S. (Johnson and Horwath Burnham, 2012).…”