Page:Popular Science Monthly Volume 86.djvu/570

566 (Fig. 2) located on an unusually low part of the bar, is said to have collapsed bodily under the blow of one very large wave; while the house shown in Fig. 5 was consumed more gradually after undermining had allowed it to tip over. Indeed, the real damage was usually accomplished independently of direct impact upon the structures themselves. Even where the beach was low and flat, as near the Octagon Hotel in the town of Seabright, the foundations were sapped from under dwellings, allowing them to tip over toward the sea; seldom if ever were these houses crushed in the first instance by the direct impact of the waves. This is clearly shown in the case of the small houses of Fig. 3, which were but a short distance from the hotel, and it is probable that the hotel itself was first weakened by the undermining process. In some cases the houses collapsed piecemeal as the sea advanced under them; or were crushed by the fall when they tipped over into the sea.

Where houses were built on pilings driven into the beach sand the removal of the sand left the buildings precariously supported on the pilings alone until shaken down by the moderate waves of some later storm. The successive stages of this process are well illustrated in Figs. 6-9, which represent four photographs of the same house. In Fig. 6 a small wave has passed through the outlying line of protecting piling and is breaking against the bulkhead built to preserve the house from destruction. Fig. 7 shows that the bulkhead has been breached and that the corner of the house is beginning to be undermined. The next figure represents a still later stage, when the sand has been removed from under most of the house, leaving it supported by the pilings alone. In this condition it fell an easy prey to the smaller waves of later storms, and Fig. 9 shows the final wreck of the building.

One reason for the destructiveness of the undermining action as compared with the direct wave attack is to be found in the fact that lines of piling and bulkheads were together able to break the force of the waves to a large extent, but could not prevent the water of each wave from washing against the foot of the low cliff, removing part of the sand, and carrying it back to sea. In many places the lines of piling, and even the bulkheads, are still in a state of partial preservation, while the cliff back of them is badly eroded and the superjacent houses completely destroyed. The fact that the houses were at a higher level than the cliffed beach was, of course, another factor which rendered direct wave impact less destructive than undermining.

Some have supposed that the active erosion of the New Jersey coast by storm waves is the natural consequence of the gradual subsidence of that coast which has been inferred by some geologists. The evidence for and against the theory of subsidence has been considered by the senior author in various publications, and need not be repeated here. Suffice it to say that the loss of land during the recent storms represents exceptionally rapid erosion of a purely temporary character,