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A method for detecting the diffusion of silver iodide particles in the atmosphere

Summary A technique is described which allows the study of the concentration of silver-iodide particles produced by a ground generator. It consists of marking these particles with Iodine 131, then filtering the air at the required places with air-borne filters. The iodine is extracted chemically, concentrated in a very small silver iodide disc which is then placed upon a nulcear emulsion. After two weeks the activity is measured by electron track counting. Limitations of the method are given.The paper has been published in extenso in the «Zeitschrift für angewandte Mathematik and Physik» (ZAMP), XIa, p. 375, 1958.     

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Zur Geologie der Danakil-Senke

Geological and geophysical investigations in the Northern part of Afar-Region were carried out by a group of scientists in 1967 and 1968. The Afar-structure is framed by the Ethiopian Highland in the West, the Somali Plateau in the South and the Danakil horst in the E. Its northern part is occupied by the NNW trending Danakil Depression (Danakil Graben), a branch of the NW trending Red Sea-Graben. The block mosaic border land in the West as well as the Danakil Alps consist of basement overlain by unfolded Mesozoic strata. Within the Afar Depression the pre-Tertiary formations are covered by limnic-fluviatile — in upper portions marine — sediments, Miocene and Pliocene in age, thickening towards the centre of the Depression. These basin fillings indicate a major phase of rift faulting prior to and during their deposition. Marginal extensions of these “Danakil-Formation” on both flanks of the Depression accompany the structural borders of the Danakil Graben, coinciding with the “outer rift structural margin” (Mohr 1967). Evaporites occupy the deepest part of the structure, “the inner Danakil Graben”, downfaulted or opened by major rift movements during Pliocene. A NW trending fault zone cutting through the flat plain north of Dallol covered by gypsum beds, seems to form the Eastern margin of the inner Danakil Graben. In its southeastern prolongation the fault and fissure system of the Amarti Volcanic Range is situated. Still active rift faulting during Quaternary caused the present topographic form of the region. These movements were followed by a marine ingression. Its sediments (Zariga-Formation, 14 C Modell ages 25 000–34 000 y) ring the depression and pass into gypsum beds towards the centre of the basin. The deepest parts of the Depression are hidden beneath the Afrera-Formation (14 C Modell ages 5800 y) framing the Lake Assale/Bakili and the Lake Afrera (soft limestones, clay and gypsum beds). The rift-forming movements in the northern Afar were accompanied by strong volcanic activity. Besides different igneous rocks intruding the pre-Tertiary and Tertiary strata of the rift margin, extensive basaltic lava flows intercalate and locally underly the Danakil-Formation. Potassium-argon age determinations on these “Afar Basalts” yielded Miocene to Pliocene age. In the southern area of the Danakil Graben the Upper Tertiary sedimentary basin fillings are replaced by “Afar Basalts” (plateau-forming flood basalt) flows. They are succeeded by scoriaceous fissure alkali-olivine-basalts and their differentiated lavas forming huge volcanoes aligned parallel to the rift structures. The Central Volcanic Range (Erta Ale volcanic chain) marking the central part of the Danakil Graben, remains active today. Besides the basaltic activity, numerous huge volcanoes display rhyolitic rocks with strong alkaline affinity.