Thick lava flows of Karisimbi Volcano, Rwanda: insights from SIR-C interferometric topography

Abstract

We use a digital elevation model (DEM) derived from interferometrically processed SIR-C radar data to estimate the thickness of massive trachyte lava flows on the east flank of Karisimbi Volcano, Rwanda. The flows are as long as 12 km and average 40-60 m (up to 1 140 m) in thickness. By calculating and subtracting a reference surface from the DEM, we derived a map of flow thickness, which we used to calculate the volume (up to 1 km 3 for an individual flow, and 1.8 km 3 for all the identified flows) and yield strength of several flows (23-124 kPa). Using the DEM we estimated apparent viscosity based on the spacing of large folds (1.2!10 12 to 5.5!10 12 Pa s for surface viscosity, and 7.5!10 10 to 5.2!10 11 Pa s for interior viscosity, for a strain interval of 24 h). We use shadedrelief images of the DEM to map basic flow structures such as channels, shear zones, and surface folds, as well as flow boundaries. The flow thickness map also proves invaluable in mapping flows where flow boundaries are indistinct and poorly expressed in the radar backscatter and shaded-relief images.

Tracking Land Use/Land Cover Dynamics in Cloud Prone Areas Using Moderate Resolution Satellite Data: A Case Study in Central Africa

“…The region has highly diverse topography, measuring 900 m above sea level at the plains in the Rift Valley to the north to the highest peak of 4507 m at Mount Karisimbi, the largest of the eight volcanoes situated in the Virunga Mountains [35]. A typical example of the complex rural landscape in western Rwanda is shown in Figure 2.…”

Deposits, character and timing of recent eruptions and gravitational collapses in Tatun Volcanic Group, Northern Taiwan: Hazard-related issues

“…Later, several methods to determine eruptive parameters based on the geometry of lava flows were devised (e.g. Moore et al, 1978;Kilburn and Lopez, 1991;Lyman et al, 1994;Stevenson et al, 1994;MacKay et al, 1998;Lyman et al, 2004). We have determined geometrical parameters of the TVG lava flows from a 1:50,000 topographic map of the area, and have calculated the parameters of their eruptions ( Table 2).…”

Emplacement of the large andesite lava flow in the Oturere Stream valley, Tongariro Volcano, from airborne interferometric radar

“…The DEM was enhanced visually using a number of standard image processing techniques: shaded relief images were generated and the light source altered to highlight the surface features, and slope and slope aspect maps were generated (e.g., Mackay et al 1998). An unweighted secondorder derivative kernel was used to identify sharp changes in slope (Lillesand & Kiefer 1994).…”

“…One of the main difficulties in obtaining a reasonably accurate estimation for the volume of a significantly thick and topographically constrained lava flow, however, is a lack of data to constrain the mean thickness at locations other than the margins (e.g., Stevens et al 1997). The second approach is a solution to this difficulty: the position of the base of the flow is modelled from measurements of the topography surrounding the lava, and subtracting this from the surface topography gives the total lava volume (e.g., Mackay et al 1998). This approach allows for the likelihood that the lava in the centre of the flow is significantly thicker than at the margins.…”