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

Abstract

The cone-building volcanic activity and subsequent erosion of San Francisco Mountain, AZ, USA, were studied by using high-resolution digital elevation model (DEM) analysis and new 40 Ar/ 39 Ar dating. By defining remnants or planèzes of the volcano flanks in DEM-derived images, the original edifice can be reconstructed. We propose a two-cone model with adjacent summit vents which were active in different times. The reconstructed cones were 4,460 and 4,350 m high a.s.l., corresponding to ∼2,160 and 2,050 m relative height, respectively. New 40 Ar/ 39 Ar data allow us to decipher the chronological details of the cone-building activity. We dated the Older and Younger Andesites of the volcano that, according to previous mapping, built the stage 2 and stage 3 stratocones, respectively. The new 40 Ar/ 39 Ar plateau ages yielded 589-556 ka for the Older and 514-505 ka for the Younger Andesites, supporting their distinct nature with a possible dormant period between. The obtained ages imply an intense final (≤100 ka long) cone-building activity, terminating ∼100 ka earlier than indicated by previous K-Ar ages. Moreover, 40 Ar/ 39 Ar dating constrains the formation of the Inner Basin, an elliptical depression in the center of the volcano initially created by flank collapse. A 530 ka age (with a ±58.4 ka 2σ error) for a post-depression dacite suggests that the collapse event is geochronologically indistinguishable from the termination of the andesitic cone-building activity. According to our DEM analysis, the original cone of San Francisco Mountain had a volume of about 80 km 3 . Of this volume, ∼7.5 km 3 was removed by the flank collapse and subsequent glacial erosion, creating the present-day enlarged Inner Basin, and ∼2 km 3 was removed from the outer valleys by erosion. Based on volumetric analysis and previous and new radiometric ages, the average long-term eruption rate of San Francisco Mountain was ∼0.2 km 3 /ka, which is a medium rate for long-lived stratovolcanoes. However, according to the new 40 Ar/ 39 Ar dates for the last ≤100 ka period, the final stratovolcanic activity was characterized by a greater ∼0.3 km 3 /ka rate.

Erosion rates and erosion patterns of Neogene to Quaternary stratovolcanoes in the Western Cordillera of the Central Andes: An SRTM DEM based analysis

“…In order to characterize the erosion pattern of the volcanoes, beside standard DEM visualization techniques (3D, shading, slope, aspect), ridge and valley detection filters (those in Karátson et al, 2010b) were also used to enhance pattern recognition. In addition, for morphometric characterization, the circularity of closed contour lines was also calculated (taking into account only the contours which encircle the whole central part of the volcano).…”

“…By contrast, the relief of Ccarhuaraso in more humid South Peru may have been overprinted by a subsequent dendritic pattern. SRTM DEM-based, slightly shaded slope maps with ridge enhancement were produced by using median difference filtering method (for details of ridge enhancement, see Karátson et al, 2010b). again.…”

Geomorphological Characteristics of the Italian Side of Canin Massif (Julian Alps) using Digital Terrain Analysis and Field Observations

“…slope maps) we used a DEM filtering method ("neighborhood statistics" in ArcView terminology) to emphasize the ridge and valley network of the studied area. The ridge and valley network can be derived from the DEM by the so-called mean difference map, which shows the elevation difference between each pixel and the mean of its circular neighborhood of radius R. If this difference is greater than a chosen positive threshold, that pixel can be classified as a ridge; if it is lower than another chosen negative threshold, it can be classified as a valley (Karátson et al 2010) As a result, sharp and high ridges as well as deep and narrow valleys are the more pronounced in this kind of map. The advantage of this method with respect to other curvaturebased ridge-enhancing processes, that the radius R can be set according to the landform scale (in this study, R was set to 450 m on an empirical base).…”

Systematic morphometric characterization of volcanic edifices using digital elevation models

“…They used a former version of the method that we here extend and describe in detail (see Section 4). Karátson et al (2010a) used DEM-based morphometry to reconstruct the shape and volume of an eroded stratovolcano. Karátson et al (2010b) used SRTM DEMs to quantify the shape of nineteen circular and symmetrical stratovolcanoes, finding two types of upper flank profiles that can be related to different dominant eruptive styles.…”