The expanding gas pushes away the overlying rock, further reducing the pressure and leading to more gas releases, and in almost no time at all half the mountain has been blown away.
42.
Hot and semi-plastic rock deep below western North America responded to the lack of compression beginning 30 million years ago by slowly rising; gradually pushing the overlying rock sideways both east and west.
43.
Towards the end of this period granite was formed beneath the overlying rocks of Devon and Cornwall, now exposed at Dartmoor and Bodmin Moor, giving rise to mineralised deposits of copper and tin.
44.
The glue-like nature of the magma generally prevents small releases of the pressure, so that only big eruptions ( those capable of ripping large vents through the overlying rock ) end up happening.
45.
Six well-preserved feathers have been recovered, indicating more complete remains of feathered dinosaurs might be found, however the site has been little-excavated, extensive removal of overlying rock has to take place before further excavation.
46.
These are younger than and stratigraphically above the breccia, but the uplift from ancient mountain-building, the dip of the beds and erosion of overlying rocks mean that the younger rocks are encountered at progressively lower altitudes.
47.
At that time the edges of the Rhine Graben were uplifted and the layers of bunter sandstone and, in places also older rocks ( Zechstein, Rotliegendes ) were exposed after the overlying rock was eroded away.
48.
Murchison thus took the Ludlow Bone Bed as the base of his Devonian Period, although over a century later this boundary was to be moved a little higher, the overlying rocks being ascribed to the Pridoli.
49.
VEI 7 or VEI 8 eruptions are so powerful that they often form circular calderas rather than cones because the downward withdrawal of magma causes the overlying rock mass to collapse into the empty magma chamber beneath it.
50.
The veins sloped downwards at angles of between 20 and 45 degrees, and to avoid the expense of removing large volumes of the overlying rock, the quarry soon became a mine, as the chambers followed the vein below ground.
