Aspectos morfometricos de los conos de escoria de Costa Rica

Abstract

33 pyroclastic cones in Costa Rica, were selected to study their morphometric characteristics. The regression obtained for the height and basal diameter ratio (H CO /W CO) is 0.17, which is in good agreement with data obtained for cones located in other places of the world. The wide dispersion found is due to differences in the factors that control eruptions that originate pyroclastic cones: ejection velocity and angle, vent diameter, etc. The analysis of the top and basal diameter ratio (W CR /W CO) and slope (S) enables the identification of several groups that broadly coincide with their position relative to the volcanic arc. Cones located in the arc constitute a heterogeneous group, in contrast to cones located as satellites in front of the arc and behind it. The former tend to have wider tops and steeper slopes than the latter. The cones in front of the arc have different sizes but a uniform W CR /W CO ratio. Back-arc cones possibly have been exposed to erosion for a longer period and are considered to be older. Correlation between cone morphology and chemical composition has been found. Cones that contain more silica and less magnesium are higher. Those containing more alkaline and less ferrous materials tend to be steeper. It is proposed that the angle of repose in the growing course of the talus depends on the viscosity of the erupting material. Nevertheless, the regressions obtained indicate only a moderate correlation; the geochemistry is considered to be just one of several factors that control the final shape of scoria cones.

Morphometric Analysis of Scoria Cones to Define the ‘Volcano-Type’ of the Campo de Calatrava Volcanic Region (Central Spain)

“…Given that many of the volcanoes analyzed in CCVR were barely 20 m high, it was necessary to automatically generate contour lines with an equidistance of 1 m from DEMs (5-m pixel resolution) in geographic information systems (GIS) (ArcMap 10.8, ESRI license for University of Castilla-La Mancha) (Figure 3). Using contour lines with an equidistance of 1 m, the morphometric measurements are much more accurate than in the traditional literature, which used maps at scales of 1:25,000 and 1:50,000 [7,12,15,24,27,33,74]. Therefore, in the preparation of the geomorphological maps of each volcano, we worked with a scale of 1:5000, which also offers much more precision when delimiting the morphology of the cone (and lava flows), and calculating parameters such as height, surface area, cone and crater diameter, etc., as has been done in other recent studies [19,20,41,42,75].…”

“…Sigurdsson et al [6] stated that these volcanoes are truncated, conical, or horseshoe-shaped and the elongated cones are built on fissures with more complex emission systems, and that scoria deposits consist of bombs, scoriaceous lapilli, and ash. Martens [15] wrote that 90% of the cones that have been observed to form were formed in less than a year and that their size is small compared to shield volcanoes and stratovolcanoes, noting that their formation originates from relatively low-viscosity magmas of basaltic composition in Strombolian or Hawaiian eruptions. Kereszturi and Nemeth [16] observed that "scoria cones are formed by 'scoria cone-forming eruptions'.…”

“…Cone slope (S co ), is the average slope of the entire surface of the volcanic edifice obtained by calculating the value of the α angle on the triangle outlined by the height and length of the volcano with respect to the horizontal line. It may be obtained from two methods: by using the cone to form a right-angled triangle and calculating the slope in degrees of one of its sides [8,44]; or by the method proposed by Hasenaka and Carmichael [12,27] and other authors [7,14,15,24,34,37,77,78]. It is calculated using the following equations:…”