The cause of major lake level changes during the evolution of Lake Van (Anatolia): internal (tectonic-volcanic) vs. external (climate) forcing

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The origin of major lake level changes during the evolution of the ca. 600 ka old (ca. 220 m drilled sediments including ca. 25% (up to ca. 500) primary and reworked tephras) fault-bound Lake Van (Anatolia) is in dispute, most interpretations invoking climate changes. I propose that tectonic factors are a plausible alternative to explain repeated major lake level changes by up to 600 m (!). The tectonic Van Basin has been geodynamically active for a minimum of 600ky. For example, a major earthquake in 2011 resulted in 600 fatalities and significant fault-displacements in the lake basin. The hypothesis presented here will be tested by high-resolution dating and textural tephra analysis at four depth ranges of major lake level change intervals. Textures of reworked tephra sourced in active subalkaline Süphan and peralkaline Nemrut volcanoes, their active flanks extending into the deep lake basin, allow unambiguous source identification while harboring much information on reworking sites and mechanisms. The reworked tephras – particularly common in the intervals of seismically documented major lake level changes – will be sampled at high resolution and analyzed texturally and compositionally in detail. We will define diagnostic criteria that allow to distinguish in-situ reworking from far-field bottom-transport processes and to correlate diagnostic reworking textures to a range of water depths as well as to rates of fast vs. slow depth changes. Such process-oriented analysis of reworked intralake tephras is novel and will aid lake tephra specialists worldwide in exploring the interpretative potential of reworked tephras. Major lake level changes will be precisely dated by 40Ar/39Ar single crystal dating of anorthoclase. This detailed age structure of drastic lake level change intervals will be compared to dated and indirectly inferred tectonic processes (e.g. rise of Ahlat Ridge-Halepkalesi lineament). Our goal is to establish the Van system as a model for broad applications of highly variable depositional modes of reworked tephra in tectonically active lake basins that have experienced major lake level and climate changes.