Chapter Twenty Three.
The Pass.
The philosophy of the movement of glaciers is but ill understood, even by the most accomplished geologists. It is supposed that the under surface of these great icy masses is detached from the ground by the thaw which continually takes place there, caused by the radiating heat of the earth. Water is also an agent in loosening their hold; for it is well-known that currents of water—sometimes large streams,—run under the glaciers. The icy mass thus detached, and resting on an inclined surface, is carried down by its own weight.
Sometimes only a very small portion of a glacier moves, causing a fissure above the part that has given way; and at other times these fissures are closed up, by the sliding of that portion next above them. An unusually hot summer produces these effects upon the glacier ice, combined with the falling of avalanches, or mountain slides, which, with their weight, serve to impel the icy mass downwards.
The weight of our three hunters was but as a feather, and could have had no effect in giving motion to the glacier; but it is possible that the gneiss rock was just upon the balance when they crossed it. Thawed around its surface, it had no cohesion with the ice on which it rested; and, as a feather turns the scale, their crossing upon it may have produced a motion, which resulted in its fall.
So vast a mass hurled into the great cleft, and acting as a driven wedge, may have been the feather’s touch that imparted motion to a section of the glacier, already hanging upon the balance, and ready to slide downwards.
Whether or not they had any agency in producing this fearful phenomenon, our travellers reflected not at the time. They were far too much terrified at the result to speculate upon causes. One after another they mounted upon the great boulder, and satisfied themselves of the facts that the crevasse had widened,—the bridge-rock had disappeared,—and their retreat was cut off!
After a little, they ventured closer to the fearful chasm. They climbed upon a ledge of the precipice, that gave them a better view of it.
From this elevation they could partially see into the cleft. At the surface it was many yards wide. It appeared to be hundreds of feet in depth. Human agency could not have bridged it. All hope of getting back down the glacier was at an end; and with consternation in their looks, they turned their faces away, and commenced ascending towards the head of the ravine.