Due for the most part to inadequate drainage of the base and side abutments, the phenomenon of uplift destabilizes gravity dams by reducing the structure's "effective weight", making it less able to resist horizontal water pressure. Uplift can act through the bedrock foundation: the condition most commonly develops where the bedrock foundation is strong enough to bear the weight of the dam, but is fractured or fissured and therefore susceptible to seepage and water saturation. According to their theories, water from the reservoir had permeated far back into the schist formation of the eastern abutment. This lubricated the rock and it slowly began to move, exerting a tremendous amount of weight against the dam, which according to the Grunskys was already becoming less stable due to "uplift". Making the situation worse, Dr. Willis established, was that the conglomerate, on which the western abutment of the dam rested, reacted upon becoming wet by swelling. In fact, the amount of swelling was such that it would raise any structure built upon it. This hypothesis was reinforced when surveys taken of the wing wall after the failure were compared with those taken at the time it was built. They reveal that in some areas the wall was 2 to 6 inches higher than when built. Therefore, the dam was caught between forces that were acting on it much like a vise, as the red conglomerate swelled on one side, and the moving mountain pressed in on it from the other. In his report, Grunsky concluded:  As soon as the dam was loosened on its base the toe of the structure spalled off. This was probably the beginning of its breaking up, and probably occurred sometime after 11:30 PM during the 23 minutes in which the water in the reservoir apparently fell 3/10 of a foot. Thereupon, quite likely, a part of the east end of the dam, meanwhile undermined, went out and the dam at this end lost its hillside support. Hydrostatic uplift at the already loose west and the weight of the remaining portion of the undermined east end caused a temporary tilting of the dam towards the east, accompanied by a rapid washing away of the hillside under the dam at its west end which then also began to break up. The reservoir water was now rushing with tremendous force against both ends and against the upstream face of all that was standing of the dam. This rush of water carried away huge blocks of concrete from both ends of the dam... There was and remains a difference of professional opinions on the amount of time that elapsed, shown by the chart made by the Stevens automatic water level recorder, from when the line indicating the reservoir level broke sharply downward until it became perpendicular.