Notice has been already taken of the shock of an earthquake, and a singular phenomenon which took place a little before midnight of Wednesday last, at Lake Merced. Before this phenomenon occurred, the lake was a beautiful sheet surrounded mostly by a fine amphitheatre of hills. It is located about seven miles from this city in a south-westerly direction, and covers a surface of about thirty acres. Various opinions have been formed realtive to this occurence; the principal one of which is, that the accumulated waters of the lake have washed away the sandy barrier by which its north-western limited was confined.
The facts of the case are simply the following: On rising from his bed Wednesday morning, Mr. Alfred A. Green stated that he had sensibly felt the shock of an earthquake at the time just mentioned, and several of the inmates of his residence made a similar statement. It was accompanied by a report like distant artillery, and was readily distinguished from the thundering of the heavy surge which constantly rolls on the sea-beach nearly two miles distant. On proceeding towards the beach, as was customary, to collect and number their horses, Mr. Green and one or two of his hired men at once discovered a wide breach in the boundary of that end of the lake nearest the ocean, and they were convinced it was caused by the shock they had felt on the previous night. Although nothing is said of any person in this city having felt the same shock there is every evidence that Mr. Green's statement is correct. That portion of the lake's boundary which has been swept away, was alluvial, and has been forming during a lapse of centuries. There is ample evidence that it was a number of feet higher than the lake itself, even when the water was the highest. It gradually sloped towards the sea-shore, which is nearly a mile from where the barrier once stood. When it was carried away it must have been done in a single moment. A passage seems to have been forced about three hundred yards in width and ten or twelve feet deep, opening on the sea-shore to the width of a mile.
Subsequently, a sort of mid-channel has been formed, commencing a short distance below the origin of the outlet, narrower and much deeper than the first, down which the water seems to have rushed with great velocity, until the lake has been emptied at least thirty feet below its previous surface. This mid-channel has gradually deepened in the centre, forming an outlet down which the waters are yet flowing into the ocean. It is very evident that if this outlet had been spontaneous, it would have been gradual, leaving no precipitous sides, looking as if immense landslips had taken place, but gradually forming a channel deepening in the centre. Nor would it have caused that loud report, or have been felt nearly a mile distant. Such things are by no means uncommon on the coast of South America. And the bed of Lake Merced may have been instantly uplifted, and as quickly have returned to its customary level; thus forcing an outlet through the heavy alluvial by which it was formerly confined. Such extraordinary phenomena have several times been witnessed in the bay of Callao and of Talcahuana. And now that the outlet has been forced, from its abrupt sides may be seen flowing the gaseous fluids which succeed earthquakes among lofty mountains—the Andes, for instance—but especially coastwise.
For two miles along the coast, on either side of the mouth of the ravine, may be seen numerous water-marks once made by the surges of the ocean. Some of them are more than a hundred feet high. And while many of these strata are horizontal, others rise or fall at an agle of forty and fifty degrees, bearing every trace that they have been tumbled about and displaced by a concussion at a much earlier period. These different strata have been froming during a lapse of centuries, while the shore had gradually been elevated. As a closing thought on this interesting phenomenon, it may be well to state that the lake was supplied only by springs and rains from the mountains. No serious danger could have been expected of a sheet of water, covering at least thirty acres—as evaporation must have been very great—unless some convulsion of nature had taken place, of which fact there are sufficient evidence.