It is obvious that the forces involved in pushing up the Andes (north south axis) to a height of 5000 m above sea- level has been, and still is continuously being sustained in the unidirectional mode. The direction of the forces will be perpendicular to the aligned axis of the mountain ranges. In this case where the collision is between a continental crust and an oceanic crust, the uplift and creation of the Andes is attributed to the noted sub-duction of the oceanic crust by the ’slab pull’ mechanism. 18,19.
In contrast, the continuing creation of the Himalayas (10,000m above sea- level) along an east west axis) is attributed to the collision between two continental crusts. It is interesting to note that the sub-duction forces (south-northeast axis) that were credited with moving India into central Asia are now not totally credited with the continuing formation of the Himalayan mountain range. The continuously compressive and possibly Isostatic forces now associated with the formation of the Himalayas appear to be far more complex than it would be if an obvious sub-duction zone was present at the India/Asia interface. van Andel 40 and Davies 8 discusses this matter in some detail. From the author’s point of view, the major significant similarity between the different orogenic activities (Andean, Himalayan and the formation of the Pyrenees) is the sustained manner of the uni-directional forces involved.