The Chyulu Hills volcanic field (Kenya): lineament traces and volcanic vents
The Chyulu Hills volcanic field (Kenya): lineament traces and volcanic vents Francesco Mazzarini, Ilaria Isola Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy Via Cesare Battisti, 53, 56125, Pisa firstname.lastname@example.org; email@example.com The Chyulu Hills, located in the eastern branch of the East African Rift System (EARS), is a northwest-southeast-aligned, elongated volcanic field almost 150 km long and up to about 30 km wide covering an area of around 2840 km^2. The volcanic field consists of numerous volcanic edifices and cinder cones and their erupted products (lava flows). These edifices form a prominent ridge of hundreds of individual and coalesced volcanoes and cinder cones that rise from the surrounding plains (<900 m above sea level) to a maximum elevation of 2175 m above sea level. This data set consists of the data collected in the CHVF by inspection of satellite imagery and digital elevation models. Data are point-like features (vent) and linear features (lineament, vent alignment and elongation). These features have been derived by i) the analysis of shaded relief images derived from the SRTM digital elevation model with a cell size of 90 m and a vertical exaggeration (3x) was used; ii) the analysis of panchromatic SPOT satellite images using Google Earth software with pixel resolution ranging from 2.5 to 20 m. The data set consists of three text files (txt file tab-delimited). All the map coordinates are in UTM zone 37S WGS84 (EPSG:32737 - WGS 84 / UTM zone 37S). For lines and elongations, the azimuth is in degree 1- Vents data set (file CHVF-vents.txt) The data sets consist of the locations (easting and northing of vent barycentre) with a clear volcanic morphology. No vents with a diameter smaller than a few pixels (i.e., less than 60 m) or disrupted vents with unclear morphology are in the data set. 2- Vent elongation and alignment data set (file CHVF-vent-elongation.txt) Vent elongation has been mapped as a line of constant length passing through the centre of the vent. Alignments of vents have been mapped only when they had a strong spatial correlation and low azimuth dispersion. 3- Lineament data set (file CHVF-lines.txt) We assumed that lineaments are the intersection of the fracture network with the Earth’s surface; we thus consider lineaments as traces of fractures and will hereafter refer to lineaments as fractures. Fracture traces have been derived by the analysis of shaded relief images derived from the digital elevation model and satellite images. Surfing in Google Earth allows complete rotation of images and the continuous variation of points of view thus providing a very useful tool for fracture mapping.