Great Disasters and Horrors in the World's History

by Allen Howard Godbey

We have already noticed that earthquakes and volcanoes are produced by the same causes; but as the myths of many nations do not connect the two, it is evident that such people did not recognize their essential identity.

But after knowing they are but variations in results, we cannot so readily explain the reason of the variations. Certain facts are well established; and from these common premises widely different conclusions have been deduced.

We know to-day that in active volcanic regions, an earthquake almost invariably precedes an eruption; and a violent one has never, within the historic period, followed an eruption. So the most reasonable inference is, that the earthquake merely betokens the presence of a vast quantity of imprisoned vapor which has not found an outlet; and that so soon as a volcanic vent is found, the pressure is relieved, and the earthquake subsides.

But this leaves us just where the theorists of volcanic agency have stopped. The question of the sudden formation of volumes of gases in sufficient quantities to produce such terrible effects is to be solved.

Mr. Mallet, who is one of the best authorities on the subject, considers that submarine eruptions must account for them. A volcanic upheaval of the sea bottom would produce crevices, by which the sea is brought directly in contact with subterranean fires. An explosion is the result, like those that have occasionally occurred at foundries from dumping masses of fiery slag into a snowbank. So what began with a gradual upheaval ends with a sudden concussion, the vibration of which passes along the sea bottom to the mainland. Every one who has lived in the city is familiar with the fact that the vibration produced by a carriage may be felt at the top of a very tall building.

But the idea that the explosion always occurs at the sea bottom leaves no way to account for the fact that a volcanic eruption acts as a safety-valve. Mr. Mallet’s conclusions are largely based on personal observations of earthquakes in England, where no active volcano exists.

That earthquakes are more violent and volcanoes more numerous on islands or near the sea coast is well-known. It is also well established that shocks frequently occur at sea, which are not perceptible on the land. The shock is similar to that produced by striking on a reef. Often have sailors been mystified, on receiving such shocks and hastily heaving the lead, to find the ocean unfathomable. Again, shocks which are most violent on land are not perceptible at sea, unless a great sea wave be produced; but such a wave in the open sea, as often experienced, produces no shock but passes under a vessel like a heavy swell. And a shock at sea is sometimes severe enough to snap a spar, or wrench loose bolts like the blow of a reef, yet no trace is perceptible on shore. Lastly, earthquakes often happen in inland regions, and affect but a small area. Clearly it will not do to attribute effects so different to explosions at the sea-bottom.

Those who attribute all earthquakes to subterranean heat and gases, whether local or general, find it easy to account for the occurrence of violent earthquakes in regions remote from active volcanoes. In case of the gradual decline of volcanic action, such as we know from the great numbers of extinct volcanoes, old trap-dykes, and ancient lava beds, to be continually taking place in one region or another, the old vents or safety-valves would cool and close. The pent up power would in consequence gradually accumulate, till finding no outlet, it would burst the crust over a wide area, and so relieve the pressure.

This finds further confirmation in the fact that the noted non-volcanic regions which are seriously shaken are all coincident with or adjacent to regions of extinct fires; while in such regions as are very seldom shaken, such as Germany, portions of North America, Brazil, the eastern slope of the Andes, the traces of such agency are less common, or of older date. Noted regions of volcanic action of comparatively recent extinction are Asia Minor, Turkey, Spain, Southern France and Greece. These, belted together by the active regions of Western Asia, the peninsula of Arabia, the Mediterranean, and Azores and Canaries, form a region which has suffered from earthquakes as much as, if not more than, any other tract upon the globe.

Those who have been puzzled by the appearance of earthquakes some distance from any actively volcanic region, have endeavored to divide earthquakes into two classes, which they have called volcanic and plutonic. This second class they have considered as originating, like the other, in the depths of the earth; but have endeavored to account for them by supposing them to be occasioned by the falling in of great caverns at a considerable depth. This theory has found a fair objection in the fact that in such cases an earthquake should always be a sinking of the ground: while the wrecking power and peculiarities of some earthquakes indicate a decided upward concussion as the first of shocks; and at the seashore, where any change in level is at once detected, upheaval is quite as common as subsidence.