オーストラリアにおける砂丘の再活動とその気候上の意義について
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The sand dunes in Australian continent have beeen classified into two kinds of shapes and origins. The moving dunes, however, are separated into two types of moving patterns and activities.<BR>The first type is called“the regional moving dune”. It means a group of dunes which are active only on their crests with weak activity and are spreaded over wide area. Its distribution is limited in the arid zone of the continent. The movement of sand on their crests is presumed not to mean the result of climatic change but to show the equilibrium condition with the present climate of the area. It is not clear, however, whether the active parts on their crests have been changed in magnitude.<BR>The second one is “the local moving dune”which means that one or some dunes are remarkably active in spite that most dunes surrounding them are tightly fixed. Their characteristics are different from those of the regional moving dunes. Namely, the local moving one is active not only on the crest but also on the side and foot, the groundswells of sand are formed on it and buried woods are scattered on its leeward. These local moving dunes which are occurring mainly both along the marginal belt of the arid zone and in the semi-arid one are observed only in the artificial areas such as pastoral land and agricultural one. It is presumed that the movement of sand on them has started recently, as some of them began their action after the trees on them had been fallen down, though almost all of them were fixed once by being covered with vegetation. It is not clesr, however, whether the movement of dunes has started or not before the artificial action was done in the areas.<BR>It is though that the climate has been so exceeding dry that the dunes which were fixed have had potential mobility in and around the semi-arid zone at least in the southern part of the continent and it is inferred that this potential mobility of some dunes has been actualized by some artificial actions from the facts as follows:<BR>The local moving dunes are distributed mainly along the critical boundary of climatic zones such as the marginal belt of the arid zone and the semi-arid one where it is extremely sensitive to both the effect of climatic change and its reflection on landform and vegetation. They are so remarkably active in movement that they would unlikely be fixed under the present natural condition and there are some dunes which are ready to be started moving among the tightly fixed ones in the area where there has been little action of man.<BR>Further, there needs more researches on the basis of the climatological and geomorphological data of the wider region including New Zealand to make clear which this climatic change toward dryness means the expansion of the interior arid zone or the desiccation of the westerly flowing from west to east along the sourthern part of the continent.
- 社団法人 東京地学協会の論文
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