Edward Whymper camped on the south-west ridge on seven
separate occasions. He reported that, on each of these occasions, late at night, there
were avalanches falling down the south face.
The greatest rock-falls always seemed to occur in the night, between midnight and daybreak. This was noticeable on each of the seven nights which I passed upon the south-west ridge, at heights varying from 11,800 to 13,000 feet.
For a time we dozed, but about midnight there came from high aloft a tremendous explosion, followed by a second of dead quiet. A great mass of rock had split off, and was descending towards us. My guide started up, wrung his hands, and exclaimed, "0 my God, we are lost!" We heard it coming, mass after mass pouring over the precipices, bounding and rebounding from cliff to cliff, and the great rocks in advance smiting one another. They seemed to be close, although they were probably distant, but some small fragments, which dropped upon us at the same time from the ledges just above, added to the alarm, and my demoralised companion passed the remainder of the night in a state of shudder, ejaculating 'terrible,' and other adjectives.These late-night avalanches were unique to the Matterhorn. Two effects combined to create this uniqueness:
GeologyThe Matterhorn and a few neighbouring peaks, including Dent Blanche, had a different origin from the rest of the Alps. In geological times the African tectonic plate collided with the European tectonic plate, over-rode it, and deposited a piece of its plate on top of the European plate.
This deposit, left stranded like a whale on a beach, eroded to form the Matterhorn and its neighbours. It was of a sedimentary origin, for it consisted of rock strata, which in the case of the Matterhorn was tilted to a significant angle, dipping a few degrees North to South and a somewhat greater amount East to West. The surrounding mountains, which formed the bulk of the Alps, had a quite different geological makeup, being igneous rock of the European tectonic plate, such as the granite of Chamounix.
TemperatureThe stratified rock structure that the Matterhorn was built from was directly affected by the daily temperature changes that alternately heated and cooled the mountain and, hence, alternately melted and refroze the mountain ice.
The south face, facing the sun, got hot through the day. At sunset it began to cool but it was midnight before the face dropped to its lowest temperature. Melt-water that had seeped into rock crevices and cracks during the day then became entirely frozen. Water on turning to ice expands, and this expansion reached its maximum once all water had become ice. The expansion caused rocks to crack and be prised apart and to loosen layers of strata. Because the south face strata had a downward dip, like tiles on a roof, some rocks dislodged. As they fell, any loose rocks in their path were swept away creating an avalanche.
the debris, which is rent off by frost, does not remain in situ, but pours down in showers over the surrounding cliffs. Each day's work, so to speak, is cleared away; the ridge is swept clean; there is scarcely anything seen but firm rock.Now consider the west face: it had a significantly steeper downward slope of its strata than the south face. It is likely, then, that late-night avalanches also occurred on this face, possibly to a greater extent than on the south face. There were no climbers on the west face, so there was no proof of such avalanches but it is a reasonable assumption.
This freezing and avalanching was the overall pattern. There were isolated parts of the mountain where the strata responded to ice formation and avalanching just as it did on the south face and, presumably, the west face, too.
The North FaceConsider the effects of geology and temperature on the north face and what bearing they may have produced at the time of the accident.
(From the Alpine Journal – vol. ii, p.154) ' ... the southern side of the mountain is raked night and day by incessant falls of stones, while on the northern side no risk is run from this source'The reason for this difference is because the strata dipped downward toward the south. On the northern side, loose rocks tended to be trapped by the angle of the strata and so avalanches were less prevalent on the north face than the south face.
But consider the very western end of the north face, i.e., the north-west corner. The strata at this point dips downward at a significant angle to the west and avalanches would be expected to occur at this corner.
Part way along the north face there is a gap or groove in the cliff. In plan it is an up-side-down U-shape. The strata of the north-east corner of this gap would dip downward at the very same angle as the north-west corner of the north face, and avalanches would be likely at this point.
How come there is this gap in the north face? It could only have come into existence because this part of the cliff was weak and friable. Ancient avalanches created the gap and likely it was still more susceptible to new avalanches than other parts of the north face.
Its surface would tend to be swept clean (similar to what happens on the south face each night and leave a solid surface that was then safe and easy to pass over). Recall Whymper's comment about the south face ridge avalanches and note its similarity to Whymper's description of the north face accident site.
The ascent of the gapThe ascent initially went up the east face until it reached a vast cliff at the top of the face. As this was too steep to climb, the ascent detoured onto the north face. Here there was also a cliff but part way across the face was the gap in the cliff that enabled access to the easier slopes above and on to the summit.
TemperatureThe north face responded to cooling just as the south and west faces did, except it happened many hours earlier. Unlike the south face, the north face only received direct sunlight in the morning, the rest of the time being in shadow. Water on the north face, therefore, froze many hours earlier than on the south face. On the north face, rock strata were loosened by the expansion of ice just as on the south face. Top | Index