4. Beautiful scenery woven together by the mountains and sea
- Theme A:
Learning about and enjoying the earth's transformation from peridotites
The landscape of Mt. Apoi Geopark in Samani is characterized by the contrast between the Apoi Mountains with sharp ridgelines and the gently sloping terrain stretching to the west. The hilly terrain is made up of sedimentary sandstone and mudstone that was deposited at the bottom of the sea about 100 million years ago during the Cretaceous Period of the Mesozoic Era and became land as a result of ground uplift and sea-level lowering caused by crustal movement. The flat parts of the four-step marine terraces* stretching from the hilly terrain to the foot of Mt. Apoi are used to sun-dry the local specialty of Hidaka Kombu kelp (also known as Mitsuishi Kombu or Laminaria angustata Kjellman) among other purposes.
Rocky monoliths are found along the coast to the west of Mt. Apo, forming a clear contrast with the gently sloping terrain. They are made up of porphyrite - a type of igneous rock that formed when magma penetrated cracks in the crust before cooling and solidifying there. The area's oddly shaped rocks are made of hard porphyrite that remained while the surrounding soft sedimentary rocks were stripped away by years of erosion. Magma intruded into cracks around 17.7 million years ago (during the Neogene Period of the Cenozoic Era) before the formation of Mt. Apoi, presumably due to crustal compression caused by the subduction of the Pacific Plate.
- *Marine terraces are a series of flat, stair-like tiers created by coastal erosion, ground uplift, and sea-level lowering caused by crustal movement. Among the four terraces, it's believed that the land at an elevation of 25 to 40 meters high includes a layer of volcanic ash from the formation of Toya Caldera that occurred around 110,000 years ago and would have been where the shoreline existed during the previous interglacial period around 120,000 years ago.