Distribution and eruptive mechanism of maars in the Kamchatka Peninsula

Abstract

Maars are monogenic volcanic edifices of peculiar morphology with a wide circular crater surrounded by a low gentle rim of erupted pyroclastic material. Craters of maars are deeply incised into underlying rocks (frequently down to the aquifer), which explains their frequent partial or complete water infill. Owing to their morphological peculiarities, maars are easily identifiable in air photos. Maars are widespread in many volcanic areas of the world, where they occur both within volcanic fields and on slopes of stratovolcanoes (craters of subsidiary eruptions). It is established that maars are formed during the highly explosive interaction between ascending magma and groundwaters. Therefore, their presence is indicative of the phreatomagmatic eruptive mechanism [11]. We present the first overview of maars of the Kamchatka Peninsula. The main purpose of this work is to estimate the role of the phreatomagmatic mechanism during eruptions of monogenic volcanoes of Kamchatka and to reveal factors controlling the geographical distribution of maar-forming eruptions. Occurrence frequency and distribution of maars. In total, 14 maars with a crater diameter of >600 m have been identified in Kamchatka using air photos and published materials [3‐8] (table). It is difficult to identify smaller maars. We believe that their number does not exceed 20. Thus, maars constitute less then 1% of the total number of monogenic volcanic edifices in the peninsula. Tuff cones and tuff rings that are composed of products of phreatomagmatic eruptions are even rarer. Other types of monogenic volcanoes dominated by cinder cones are related to eruptions characterized mainly by the magmatic mechanism of magma fragmentation [11]. Hence, eruptions with a prevalent phreatomagmatic eruption mechanism are rare in Kamchatka. The geographic distribution of maars throughout the Kamchatka Peninsula is very irregular (Fig. 1), with their concentration being independent of the total number of monogenic edifices in particular areas. For example, the Klyuchevskaya group of volcanoes hosts numerous monogenic cinder cones, but maars are lacking here. They are also extremely scarce in the Sredinnyi Range (Kamchatka), where intense volcanism produced numerous isolated cinder cones, lava flows, and extrusive domes. Inasmuch as phreatomagmatic eruptions require water, in addition to magma, we attempted to estimate the influence of this factor on the localization of maar-forming eruptions in Kamchatka.