GIS methods applied to the degradation of monogenetic volcanic fields: A case study of the Holocene volcanism of Gran Canaria (Canary Islands, Spain)

Abstract

Modeling of volcanic morphometry provides reliable measurements of parameters that assist in the determination of volcanic landform degradation. Variations of the original morphology enable the understanding of patterns affecting erosion and their development, facilitating the assessment of associated hazards. A total of 24 volcanic Holocene eruptions were identified in the island of Gran Canaria (Canary Islands, Spain). 87% of these eruptions occurred in a wet environment while the rest happened in a dry environment. 45% of Holocene eruptions are located along short barrancos (S-type, less than 10 km in length), 20% along large barrancos (L-type, 10–17 km in length) and 35% along extra-large barrancos (XL-type, more than 17 km in length). The erosional history of Holocene volcanic edifices is in the first stage of degradation, with a geomorphic signature characterized by a fresh, young cone with a sharp profile and a pristine lava flow. After intensive field work, a careful palaeo-geomorphological reconstruction of the 24 Holocene eruptions of Gran Canaria was conducted in order to obtain the Digital Terrain Models (DTMs) of the pre- and post-eruption terrains. From the difference between these DTMs, the degradation volume and the incision rate were obtained. The denudation of volcanic cones and lava flows is relatively independent both their geographical location and the climatic environment. However, local factors, such as pre-eruption topography and ravine type, have the greatest influence on the erosion of Holocene volcanic materials in Gran Canaria. Although age is a key factor to help understand the morphological evolution of monogenetic volcanic fields, the Gran Canaria Holocene volcanism presented in this paper demonstrates that local and regional factors may determine the lack of correlation between morphometric parameters and age. Consequently, the degree of transformation of the volcanic edifices evolves, in many cases, independently of their age.

Introduction

Geographic Information Systems (GIS) provide a suitable methodological setting for the elaboration of morphometric models of volcanic eruptions, both for aggradation and for degradation processes. Morphological parameters and their derivatives can be more accurately determined with GIS than with traditional geometric methods (Rodriguez-Gonzalez et al., 2010).

Detailed cartography of the common units in monogenetic volcanic fields (cones, lava flows and pyroclastic sheet-like fall deposits), together with geomorphological and stratigraphical observations of these units and the surrounding substrate, combine to obtain Digital Terrain Models (DTMs) of the three different evolution stages of the studied area: pre-eruption, post-eruption and present-day. Comparisons of these DTMs in a GIS framework give 2D and 3D models allowing a proper understanding of the topographic changes that have taken place in the areas affected by volcanic eruptions, both in construction stages and in their subsequent degradation. The comprehension of these topographic changes facilitates assessment of the associated hazards and the design of mitigation plans (Holcomb, 1987, Thouret, 1999, Pareschi et al., 2000, Inbar and Risso, 2001, Carracedo et al., 2004, Renschler, 2005, Harris et al., 2007, Rodriguez-Gonzalez et al., 2009).

Morphometric studies of monogenetic volcanic fields are common in the scientific literature for determining morphological parameters (e.g., Wood, 1980a, Wood, 1980b, Wilson and Head, 1983, Rowland et al., 1999, Rowland et al., 2003, Harris et al., 2007) or focusing on pyroclastic stratigraphic relationships (e.g., Martin and Németh, 2006, Manville et al., 2009, Németh, 2010). Most of the monogenetic volcanic fields studied are located in an almost flat relief where the pre-eruption topography exerts a weak influence on the aggradation and degradation of volcanic landforms (e.g., Wood, 1980a, Wood, 1980b, Rowland et al., 1999, Walker, 2000, Martin and Németh, 2006). Nevertheless, in an intraplate oceanic volcanic island setting, mainly islands in a rejuvenated stage where erosion processes predominate over the volcanic ones, the pre-eruption relief greatly influences the distribution and morphology of monogenetic volcanoes (e.g., Macdonald et al., 1983, Walker, 1990, Carracedo et al., 2002, Carracedo and Tilling, 2003, Guillou et al., 2005, Legendre et al., 2006).

The Gran Canaria Holocene monogenetic volcanism happened on an island in an advanced rejuvenated stage, with a dense radial network of deep ravines forming a rugged relief. In a previous paper we presented the palaeo-geomorphological reconstruction of the aggradation parameters in this volcanic field (Rodriguez-Gonzalez et al., in press). The aim of this paper is to determine the degree of denudation of these Holocene volcanic forms by applying this proven methodology (Rodriguez-Gonzalez et al., 2010).