Today's photo is a little to the left and a tighter shot of the hills of the Gunung Mulu National Park of the photo I posted a few days back.
To the right you can see examples of the limestone cliffs that feature in this area (they're on the left in the photo I posted earlier). Up in the hills in the top left corner you can see a collapsed surface. These highlight some of the challenges of hiking in this area. The terrain makes it extremely difficult but you could be hiking along and find yourself on the edge of a cliff. Being so far from help, that's why you stay on the trails.
The rocks here are soft limestones and sandstones. Mount Mulu itself is sandstone so this area has seen some major tectonic activity resulting in the lifting of the rock layers followed by massive erosion. The frequent and heavy tropical rains have eroded both mechanically and chemically these soft rock layers to form these hills and valleys, and the caves that lay beneath them, aided by the cracks in the rock layers. The erosion in the top left of the photo is almost certainly caused by heavy water run-off from the hills above finding and enlarging a stress fracture in the rock to the point that this chasm now exists.
The caves of Mulu themselves became known of in the 1850s because the explorers of the day noticed rivers and streams disappearing underground or emerging from the base of cliffs in the area. Some of the passages at Mulu are so massive because of the sheer volumes of water that fall here when it rains. I mentioned before that I started caving in the Mendip hills of england in the 1970's. While people in england think its rains a lot there, in reality, compared to the tropics of South East Asia, it does not – nowhere near as heavy for nowhere near as long.
Indeed, I find myself bemused and concerned at how little an amount of rain is needed in the UK now to cause massive flooding. Here on the Texas Gulf Coast we'll get as much rain from a storm cloud in an hour as the UK will see in a bad day. Now that's rain but it's still nothing compared to a monsoon rain event in Borneo!
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