Geological History of Tosashimizu (1)
From the depths of the ocean
The land that present-day Tosashimizu stands on began to form approximately 38 million years ago as a result of the movement of tectonic plates. An oceanic plate descended beneath a continental plate, a process that over some 21 million years gradually caused sediment from the oceanic plate to come loose and accumulate onto the continental plate. A new geological body, a so-called accretionary wedge, slowly formed at the tip of that plate. As the accretionary wedge grew, parts of it gradually emerged from the ocean to form new land.
Through shallow waters
As the accretionary wedge grew, shallow seas materialized along the edge of the continental plate. Sand and mud began to accumulate in these coastal waters approximately 17 million years ago, gradually hardening into new geological strata. These strata are collectively known as the Misaki Group and took shape around the time when land at the edge of mainland Asia broke off into the ocean and formed the Japanese archipelago. The Misaki Group contains traces of this great upheaval, and is a source of significant interest for geologists. The strata offer a chance to study what the environment around the Japanese islands looked like at a time when the archipelago was still moving toward its current position.