Wells often appear to be acted upon in the same manner as springs.
At the time of the California earthquake (April, 1855), the level of the water in certain wells was raised ten to twelve feet.
A consequence of the earthquake at Neufchâtel, in 1749, was to fill some of the wells with mud.[65] At Constantinople, on September 2, 1754, wells became dry.[66]
Explanation of the above phenomena.—That the water in springs and wells should be caused to rise at the time of an earthquake, admits of explanation on the supposition of compressions taking place similar to those which cause the rise of water in fissures. That the water in wells and springs should be rendered turbid, is partly explained on the supposition of more or less dislocation taking place in the earthy or rocky cavities in which they are contained or through which they flow.
At the time of a large earthquake it is extremely probable that there is a general disturbance in the lines of circulation of subterranean waters and gases throughout the shaken area. By these disturbances, new waters may be brought to the surface, two or more lines of circulation may be united, and the flow of a spring or supply of a well be augmented. Fissures, through which waters reached the surface, may be closed, wells may become dry, or springs may cease to flow, hot springs may have their temperature lowered by the additions of cold water from another source, and, in a similar manner, waters may be altered in their mineralisation. An important point to be remembered in this consideration is the mutual dependence of various underground water supplies, and the area over which any given supply may circulate. A well in the higher part of Lincoln Heath is said to be governed by the river Trent, which is ten miles distant; when the river rises the well rises in proportion, and when the river falls the water in the well falls.[67]
The change which is usually observed in hot springs is, that before or with earthquakes they increase in temperature, but afterwards sink back to their normal state. This increase in temperature may possibly be due to communication being opened with new or deeper centres of volcanic activity, or a temporarily increased rate of flow.
That the water issuing from newly formed fissures or springs should be hot, might be explained on the supposition of its arising from a considerable depth, or from some volcanic centre. It might also be attributed to the heat developed by friction at the opening of the fissures. These changes which earthquakes produce upon the underground circulation of waters are phenomena deserving especial attention. Although we know much about the circulation of surface water, it is but little that we yet know about the movement of the streams hidden from view, from which these surface waters have their sources. Earthquakes may be regarded as gigantic experiments on the circulatory system of the earth, which, if properly interpreted, may yield information of scientific and utilitarian value.
The sudden elevations, depressions, or lateral shifting of large tracts of country at the time of destructive earthquakes are phenomena with which all students of geology are familiar. In most cases these displacements have been permanent; and evidences of many of the movements which occurred within the memory of man, remain as witnesses of the terrible convulsions with which they were accompanied.
Movements on coast lines and level tracts.—At the time of the great earthquake of Concepcion, on February 20, 1835, much of the neighbouring coast line was suddenly elevated four or five feet above sea level. This, however, subsequently sank until it was only two feet. A rocky flat, off the island of Santa Maria, was lifted above high-water mark, and left covered with ‘gaping and putrefying mussel-shells, still attached to the bed on which they had lived.’ The northern end of the island itself was raised ten feet and the southern extremity eight feet.[68]
By the earthquake of 1839, the island of Lemus, in the Chonos Archipelago, was suddenly elevated eight feet.[69]