Abstract
The terrestrial 3D Laser Scanning technique has been applied to analyse the surface roughness of pyroclastic deposits on volcanic surfaces at Mt. Etna. This technique allowed the construction of high accuracy digital elevation models of small surfaces, about 1 m across. Sampled surfaces differ for percentage of coverage and for grain size of the pyroclastic deposits. The change in grain size distribution for the pyroclastic unconsolidated deposits affects the surface roughness. The roughness of the site where the finest pyroclastic deposits occur is mainly governed by large scale wavelength morphology (Hurst exponent H = 0.77 for lengths larger than 16 mm). The other sampled surfaces have self-affine characters with low (0.15) to intermediate (0.35 - 0.38) Hurst exponents for lengths higher than 10 22 mm. Here we show results of the analysis of the surface roughness of the pyroclastic deposits emplaced during the 2001 and 2002-2003 eruptions at Mt. Etna. Grain size and thickness of pyroclastic deposits mainly control the overall roughness of such as volcanic surface.
Highlights
The roughness of natural surfaces on the Earth and on terrestrial planets is defined as the topographic expression of a surface at horizontal scale from sub-metre to hundreds of metres (Shepard et al, 2001)
Topographic data for wide areas are derived from optical and radar sensors mounted in airplane or satellite platform in planetary geology and in volcanology
Following the Rayleigh Criterion, a surface is smooth if h < l/8cosq, where h is the standard deviation of surface relief and q is the incident angle; surface roughness is crucial for microwave applications since the used wavelengths may vary between 1 to 100 cm
Summary
2003; Mazzarini et al 2005; 2007; Morris et al, 2006). In the field of volcanology, the structure and roughness of lava flows provide information on flow emplacement parameters and on flow rheology (Bulmer et al, 2001; Morris et al, 2006; Pesci et al, 2007), or defining ground deformation patterns in lava fields by using InSAR data (Briole et al, 1997; Amelung et al, 2000; Froger et al, 2001; Stevens et al, 2001). The surface topography was acquired by using a portable terrestrial 3D Laser Scanner, producing detailed digital elevation models of volcanic surfaces up 0.7 m wide with vertical resolution less than 0.5 mm. This contribution focuses on pyroclastic deposits (scoriae, lapilli and ash) erupted in the last few years (2000-2003) that mantled the eastern and southern flanks of the volcano (Andronico et al, 2005; Casacchia et al, 2006; Sgavetti et al, 2006). All the measurements have been collected using the WIDE lens in use with the instrument
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