Erosion calderas: origins, processes, structural and climatic control

Abstract

The origin and development of erosion-modified, erosion-transformed, and erosion-induced depressions in volcanic terrains are reviewed and systematized. A proposed classification, addressing terminology issues, considers structural, geomorphic, and climatic factors that contribute to the topographic modification of summit or flank depressions on volcanoes. Breaching of a closed crater or caldera generated by volcanic or non-volcanic processes results in an outlet valley. Under climates with up to F2000-2500 mm annual rainfall, craters, and calderas are commonly drained by a single outlet. The outlet valley can maintain its dominant downcutting position because it quickly enlarges its drainage basin by capturing the area of the primary depression. Multi-drained volcanic depressions can form if special factors, e.g., high-rate geological processes, such as faulting or glaciation, suppress fluvial erosion. Normal (fluvial) erosion-modified volcanic depressions the circular rim of which is derived from the original rim are termed erosion craters or erosion calderas, depending on the pre-existing depression. The resulting landform should be classed as an erosion-induced volcanic depression if the degradation of a cluster of craters produces a single-drained, irregular-shaped basin, or if flank erosion results in a quasiclosed depression. Under humid climates, craters and calderas degrade at a faster rate. Mostly at subtropical and tropical ocean-island and island-arc volcanoes, their erosion results in so-called amphitheater valleys that develop under heavy rainfall ( 1 F2500 mm/year), rainstorms, and high-elevation differences. Structural and lithological control, and groundwater in ocean islands, may in turn preform and guide development of high-energy valleys through rockfalls, landsliding, mudflows, and mass wasting. Given the intense erosion, amphitheater valleys are able to breach a primary depression from several directions and degrade the summit region at a high rate. Occasionally, amphitheater valleys may create summit depressions without a pre-existing crater or caldera. The resulting, negative landforms, which may drain in several directions and the primary origin of which is commonly unrecognizable, should be included in erosion-transformed volcanic depressions.

Late-stage volcano geomorphic evolution of the Pleistocene San Francisco Mountain, Arizona (USA), based on high-resolution DEM analysis and 40Ar/39Ar chronology

“…These erosion calderas are typically much older (e.g., the 1.5 Ma Mt. Taylor in New Mexico: Perry et al 1990;Love and Connell 2005; for other examples, see Karátson et al 1999). At SFM, dominance of glacial resculpturing over fluvial erosion is also shown by the broad outlet of the Inner Basin (Figs.…”

“…4b), and one of these, category 1, is associated with (a) flat bottom of cirques and glacial valleys and (b) ring plain (of volcaniclastic and fluvial apron). A flat interior is absent in fluvially modified erosion calderas where a dendritic drainage pattern has usually developed (Karátson et al 1999). These erosion calderas are typically much older (e.g., the 1.5 Ma Mt.…”

“…At SFM, dominance of glacial resculpturing over fluvial erosion is also shown by the broad outlet of the Inner Basin (Figs. 2, 3, and 4), a feature that never appears in real erosion calderas (Ollier 1988;Karátson 1996;Karátson et al 1999).…”

“…The depression hosted a number of glaciers (Updike 1977) whose cirque walls and moraines are still visible. Due to the obvious post-collapse erosion, Holm (2004) considered the Inner Basin as an "erosion caldera," although it lacks the typical fluvial erosional dissection and modification defined for erosion calderas by Karátson et al (1999). However, the contribution of erosional modification as well as the role of glacial vs fluvial erosion in forming the present-day Inner Basin has not been clarified.…”

“…Planèze analysis Under semihumid to dry climates, remnants of original cone surfaces may be found as planèzes or flatirons (Ollier 1988;Karátson et al 1999). These are polygonal, preferably triangular flank segments that remain relatively undissected between the pathways of fluvial (or glacial) erosion (Cotton 1952;Ollier 1988).…”