The Nuée Ardentes of Sabalan Volcano in Iran

Abstract

This article deals with the introduction and explanation of the two nuéeardentes of "Mue'el Valley" and "Shirvandareh Valley" which are one type of the pyroclastic flows of Sabalan volcano. One of the features of nuéeardente in these two valleys is the presence of large blocks in upstream of valley and the abundance of ash in downstream which it has happened in one stage in Mue'el and in several stages in Shirvandareh Valley. Considering the antiquity of the great Sabalan volcano and numerous changes that have happened during these long years in the region, determining the temperature of nuéeardente was impossible. But what could be mentioned as a sign of high temperature because of nuéeardente is the presence of rust ground mass on piece levels which indicate hot water steam (500˚C to 600˚C). Also puzzle breakings like those in these rocks should be the result of severe explosion blast and very fast movements of nuéeardente that has broken these rocks instantly. These nuéeardentes are peléan type and they are more or less synchronous, and the main reason could be the huge explosion which happened because of the second caldra's subsidence. By comparing deposits of the two nuéeardentes of Mue'el Valley and Shirvandareh Valley, it is observed that the extent, thickness, and size of blocks are higher in Shirvandareh than those in Mue'el Valley. Also considering higher levels of pieces' adherence and hardness of deposits, it can be concluded that the temperature of this complex was higher than that of Mue'el Valley, and in general the power of Shirvandareh's nuéeardente is more than the Mue'el Valley's.

Geochemical Characteristics of Sabalan Volcanic Rocks in Northwestern Iran​

“…Radiometric age of these rocks is 5.2 Ma (Mousavi, 2013). During this stage, thick, extensive ash fl ows and glowing cloud deposits (Fahim Guilany et al, 2016) as well as lava fl ows mainly of trachyandesitic composition, erupted possibly from several centers and brought a large volcanic complex reaching a great thickness (Alberti et al, 1976). The above mentioned lavas are more than 50 m thick and spread over 10 km.…”

“…One of the most important issues in Sabalan volcanic activity is the presence of pyroclastic air-fall and base surge deposits, nuée ardentes, and ignimbrites that formed a volume more than 14 km 3 in area (Fahim Guilany et al, 2016) (Figure 3). Because of its potential volcanic hazards and geothermal potential, Sabalan volcano is an imperative object of study.…”