Application of a GIS algorithm to delimit the areas protected against basic lava flow invasion on Tenerife Island

Abstract

A GIS algorithm has been applied to analyse the maximum potential extent that lava flows can reach in order to delimit the areas topographically protected against flow invasion. The algorithm selected makes use of a special kind of spatial analysis functions called neighbourhood operators, in which the outcome depends on the values that one or more specified variables adopt in the surroundings of the element where analysis takes place. Assuming the maximum magnitude hypothesis, potential lava flow invasion areas can be calculated with spatial analysis functions in the context of two propagation regimes: persistent flow lengthening, and a combination of persistent flow lengthening and widening. To define the algorithm behaviour for each regime, a series of simple stochastic rules have been set to establish the way in which lava flow propagation can proceed. The algorithm has been applied on three source areas located in Tenerife Island characterised by their high probability of occurrence of basic effusive events. For each area, maximum potential flow extent has been calculated following both propagation regimes, with the aim of delimiting the areas that would potentially remain out of lava reach. No distance limits have been taken into account to carry out the calculation, as lava has on many occasions reached the coastline either in historic or geologic times. An additional hazard exposure level analysis has been possible in those areas where results indicated that flows could potentially arrive from more than one source. Algorithm performance assessment has been carried out in terms of accuracy by generating a series of 3D views and comparing the algorithm application results with those obtained from stochastic physical model simulation. Although the GIS algorithm applied does not distinguish the probability level of an area being invaded by lava, it has clearly identified on Tenerife the areas which are potentially safe from the flows that could originate at any point located inside or on the margins of each of the source areas considered. This capability can be advantageously used to develop medium- to long-term risk prevention and management measures.