Remote sensing study of sector collapses and debris avalanche deposits at Oldoinyo Lengai and Kerimasi volcanoes, Tanzania

Abstract

Evidence for volcano collapse and debris avalanche deposits (DADs) at Oldoinyo Lengai (OL), Tanzania, has been obtained from mapping and fieldwork. Three major DADs have been identified, named Zebra, Cheetah and Oryx DADs. Field evidence indicates geologically young ages. On this basis a remote sensing (RS) study of the active carbonatite volcano OL and the surrounding rift plain was carried out, using Shuttle Radar Topography Mission (SRTM) digital elevation data, Landsat and ASTER imagery, geological maps and aerial photographs. The SRTM digital elevation model (DEM) allowed morphological characterization of OL and reassessment of the volcano volume to 41¡5 km 3 . This enabled the identification of collapse scars, fields of large hummocks (.300 m across), sharp deposit edges typical of DADs, and estimation of the minimum thickness of the DADs. Multispectral and topographic RS data interpretation allowed mapping of the extent and estimation of the volume of two sector-collapse scars and three DADs. The DADs extend up to 24 km from OL and have volumes ranging from 0.1 to ,5 km 3 . Striking radial ridges and grooves were identified in some parts of the DADs. The morphological variability for ridges and grooves in different DADs is attributed to contrasting flow dynamics and avalanching material. A volcano collapse and the corresponding DAD, ,1 km 3 in volume, were also characterized by RS at the nearby Kerimasi volcano. The presence of young DADs highlights the need for routine monitoring of ground deformation and seismicity at OL to anticipate hazardous events.

Melilite-group minerals at Oldoinyo Lengai, Tanzania

“…Phonolites dominate the southerly Lengai I (Klaudius and Keller, 2006). The cone of the superimposed Lengai II developed after a major cone collapse of Lengai I (Klaudius and Keller, 2006), which occurred ≥10,000 years BP (Klaudius and Keller, 2004;Kervyn et al, 2008) with related debris avalanche deposits extending about 25 km north into Lake Natron. Lengai II is characterized by its extremely peralkaline combeitewollastonite nephelinites, the most recent of which are melilite-bearing, especially the products of the 1940/41, 1966/67 and 2007/08 eruptions (Dawson et al, 1992;Mitchell and Dawson, 2007;Keller et al, 2010).…”

Fundamental changes in the activity of the natrocarbonatite volcano Oldoinyo Lengai, Tanzania

“…At least three debris avalanche deposits were identified to have occurred in the last 10 ky (Klaudius and Keller 2004;Kervyn et al 2008b). One of these is a largescale sector collapse of ∼5 km³ that affected a major part of the N flank.…”

Volcanic facies of the debris avalanche deposit of Tata Sabaya Volcano, Central Andes.

“…En la parte proximal de estos depósitos, se ha observado grandes bloques rotados (e.g., Wadge et al, 1995;Voight et al, 2002;Ponomareva et al, 2006) similares a los bloques Toreva caracterizados por Reiche (1937). Una particularidad de este tipo de depósitos es que, tanto en el interior de los cerrillos como en el de los bloques Toreva, es posible reconocer la composición del material colapsado y, en ocasiones, las relaciones estratigráficas de los materiales que fueron incorporados en el momento del colapso del volcán (e.g., Malone, 1995;Wadge et al, 1995;Belousov et al, 2001;Clavero et al, 2004;Kervyn et al, 2008).…”

“…Debido a esto, para su estudio es común la utilización de sensores remotos tales como fotografías aéreas, imágenes satelitales Landsat MSS, TM e imágenes satelitales ASTER (e.g., Francis et al, 1985;Francis y Wells, 1988;Kervyn et al, 2008).…”