Physical Volcanology of the Cora Maar, Erciyes Volcanic Complex

Abstract

Cora Maar (CM) is a monogenetic volcano located to the 20 km northwest of Mount Erciyes, within the Cappadocial Volcanic Province (CVP). Cora Maar is typical example of a maar-diatreme volcano with a nearly circular crater with a mean diameter of c. 1.2km. The CM crater is surrounded by a well-bedded basesurge tephra rim sequence up to 40m in thickness. This sequence is subdivided into various facies depending on the characteristics of the contituents. Having a D/d ration of 12, Cora is a relatively mature maar compared to recent maar craters in the world. Cora crater is excavated within the andesitic lave flows of Quaternary age. The tephra sequence is not indurated and consists of juvenille scoria clasts up to 70cm, lithis clasts up to 130cm, accretionary lapilli up to 1.2cm in diameter, and ash-lapilli sized volcanic material. Accretionary lapilli are observed in almost every level of the sequence and classified as rim and core-type. Base surgery layers display well-developedantidune structure indicating the direction of the transport. Both progressive and regressive dune structures.Observed vertical and lateral facies change in bedding style of base surge deposits can be explained by the decrease of the surge flow power and due to a decrease in suspended-load transport rate and/or an increase in bedload transport rate, respectiively. Detailed sections were made bed by bed from 5 different locations from CM tephra. These sections were measured and sampled for granulometric analyses alon a 400m tephra profile 500, 750, 1000m distance from the crater. A total of 168 samples were sieved with mesh ranging from Phi = -5 - +4 (32mm-1/16mm0. According to granulometric analyses, samples plot within the base surge field in sigma(Phi) vs. Md-Phi diagram. CM samples display a bimodal distribution with a wide range of Md values, characteristic for the surge deposits. Very poorly sorted, biomodal ash deposits generally vary from coarse tail to fine tail grading deoending on the grain size distrubution while very poorly sorted lapilli and block-rich deposits display a positive skewness due to the fine tail grading.