オーストラリア南部における最近の砂丘活動と降水量変動との關係

抄録

For the remobilization of dunes in the southern part of Australia, many causes have been pointed out. The climatological cause, however, has been discussed only insufficiently. In this paper the relationship between the recent dune activities revealed by geologic, geomorphologic, vegetation and hearing surveys, and the rainfall fluctuations induced by the analysis of both instrumental data and drought records was examined.
It was confirmed that the patched distribution of presently active dunes with a sharp contrast to the surrounding stable dunes covered with vegetation in the semi-arid and humid zones is not due to the local difference in climate, but due to the patched distribution of thickness of the latest Pleistocene to late Holocene dune sands. Although some of presently active dunes are reported to have been active even before the European settlement, most of them started their sand drifts after the vegetation clearance by them. Therefore, almost all of them can be called “remobilized dunes”.
The marked dune activities have been taking place whenever the residual mass curve of rainfall continuously decreased for more than one year resulting in the amount of the sum of the decrease exceeded 500 and/or 600‰ of the mean annual rainfall of each region. It is since the end of the 19 th century that the periods of decreasing in rainfall and severe droughts, when marked sand drifts also occurred, became frequent in the southern part of Australia. It was relatively humid from the end of the 18th century to the end of the 19th century and the dry phase started from the beginning of the 20th century. The remobilized dunes have increased in both number and coverage since the beginning of the 20th century when the dry climate became more frequent. This circumstance continues now at least in the southern part of Australia.