Tors on the Old Man Range

The tors are tall, isolated rock outcrops, sculpted out of schist that has been eroded and weathered into remnant stumps of bedrock. These once joined up as a continuous rock formation. The flat surface of the landscape here (as on the tops of the other Otago ranges) is an ancient erosion surface called the Waipounamu Erosion Surface. It dates from the time when the continent of Zealandia was planed off by advancing seas as it sank after its separation from Gondwanaland, between about 85 to 25 million years ago.The last shaping of the landscape and tors was done in the Pleistocene Ice Ages.

As you admire these magnificent rock formations, spend some time trying to imagine them being formed. There are lots of possible erosion and weathering processes that may have been involved. What was the part played by water, ice, wind, freezing and thawing, or the relative hardness or softness of different parts of the schist? in places on the surfaces of the tors you can see small circular rock basins that are known to have taken tens of thousands of years to form by the action of freezing and thawing of ice on the rock surface.