Holocene development of mountain wetlands within and outside of landslide in the Hachimantai volcanic group, northeastern Japan

Abstract

In warm and humid, tectonically active regions like Japan, landslides are an important influence on the development of mountain wetlands, but data bearing upon the relationship of Quaternary landslides to wetland development are scarce. We used lithological analysis, 14C dating, tephra age data, and carbon contents of wetland cores to compare the evolution of four wetlands, one (the Oyachi wetland) within a landslide area transformed by mass movement and three (the Appi Highland wetlands) outside of a landslide area, in the heavy snowfall region of the Hachimantai Mountains of northeastern Japan. Evidence from the Oyachi wetland shows that its transition from peatland to forest was interrupted at about 5500 cal BP by slope movement leading to the development of a lake that was drained by streams at about 3300 cal BP, after which a peatland environment has persisted until the present. We suggest that the evolution of this type of wetland is primarily influenced by landslide movements and stream dissection rather than climate change. In the Appi Highland wetlands, peatlands appeared much later, around the time of the To-a tephra fall in 915 AD, during the Medieval Warm Period, and have persisted with little change until the present. We suggest that the development of mountain wetlands outside of landslide areas is primarily related to climate changes rather than topographic changes. Sediment analyses of mountain wetlands within landslide areas may be useful for tracing the development of Quaternary landslides and subsequent topographic changes that may have implications for biodiversity in mountainous regions.