Introduction

The semi-circular Avike Bay at the fast rising coast of the Bothnian Sea has previously been investigated to show its formation as a caldera related to Alno intrusives and for prospecting of mineral deposits. In this presentation the Avike Bay is suggested to be caused by an impact event.

Studies have been made of the rock physical properties based on in-situ measurements and laboratory measurements of rock samples. The shore and some of the islands have been searched several times for finds of potential impactites and a team of divers has collected samples from the shallow sea floor. At one outcrop, an enigmatic breccia was found that further strengthened the suspected impact connection of the structure. Aeromagnetic measurements indicate an anomalous pattern of magnetic structures within the bay. Gravity measurements across the bay on ice have been planned for several winter seasons, but still await an occasion with sufficient thickness of the ice. This report gives an acccount of the information so far collected and its interpretation with respect to a possible impact origin of the Avike Bay structure.

Fig. 1. Impact structures in Fennoscandia. The Avike Bay structure is located at the western shore of the Bothnian Sea. Modified from Abels et al. (2002).

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