Cascading landscape geochemical systems of volcanic islands (case study of the Matua Island, the Сentral Kuril Islands)

Possible application of the concept of cascading landscape geochemical systems (CLGS) in relation to islands with active volcanoes is analyzed. The object of the study is the Matua Island with the Sarycheva volcano, which is the most active within the Kuril Islands. The structure of the island’s CLGS has three altitudinal levels which differ in morphological and lithological base, exogenous processes, vegetation cover and the elements’ migration conditions. It was found that the main lateral flows connecting all levels are the gravitational displacement of tephra, underground runoff with discharge in the lower level at the contact of marine terraces, as well as volcanic mudflows. The surface runoff is almost completely absent, due to high permeability of the soil-pyroclastic cover; as a result, there are no typical catenae associated with water runoff. It is shown that the volcanic CLGS is characterized by pulsing functioning and different types of lateral flows during and between the eruptions. During the period of volcano activation, aerial and gravigenic flows, such as tephra deposition and associated pyroclastic flows and waves, lava flows, gas emissions and lahars, prevail, the solid matter is forced into the mechanical migration. The flows connect the geochemical landscapes of all levels, i.e. upper, middle and lower, and reach the adjacent marine area. During the periods between eruptions, the role of modern exogenous processes, namely avalanches, mudflows and rock falls, and underground water increases; new lateral connections are being formed within the island CLGS. The coastal zone is a characteristic structural element of the CLGS of all volcanic islands. Specific features of its structural and functional organization are determined by multidirectional flows of matter with different chemical composition from the volcanic core and from the ocean, which results in a heterogeneous and mosaic landscape-geochemical structure.