The Wonder Book of Volcanoes and Earthquakes

by Edwin J. Houston

Another great seaquake, known as the Iquiqui seaquake, during 1868 in the same neighborhood damaged severely the towns of north Chile and southern Peru.

While, however, there is difficulty in readily observing the earthquake waves that form in the deep ocean, yet such is at times the violence of an earthquake that there is no difficulty in detecting its presence, even in deep water. Dr. Rudolph has made a careful study of the evidences of earthquakes produced in the deep sea, from a careful examination of a great number of the logs of ships. Logs, as everybody knows, are books in which the captain or commanding officer makes careful entries of all important happenings to the vessel, conditions of the weather and of the sea. From this source Dr. Rudolph obtained considerable information of much value concerning these phenomena.

I have already called your attention to portion of the Atlantic Ocean lying near the Equator, in the warmest part of the ocean, between Africa and South America, as being a region especially liable to submarine volcanic showers. While, generally speaking, there is nothing in this region to indicate the probability of submarine disturbance, yet suddenly, if a vessel happens to pass directly over the point of origin of the quake, there ensues a great quaking or quivering. Loose objects on the ship begin to shake and clatter. Noises arise from some invisible point deep down in the ocean. The disturbance grows, the noises begin to resemble distant thunder, the ship trembles and staggers as though it had struck rocks, and many believe she is about to go down; when, as suddenly as it began, the commotion ceases, the noises stop, and the ship shapes her course as calmly, and as gallantly, as before.

Rudolph gives two excellent examples of seaquakes in this region, both of which were, doubtless, due to submarine eruptions.

On the 25th of January, 1859, as the ship Florence was in lat. 0° 48' N., long. 29° 16' W., about ten miles N. W. by N. from St. Paul's Rock, the people on board felt a sudden shock that began with a rumbling sound like distant thunder. This lasted only forty seconds. The glass and dishes of the vessel rattled so violently that it was feared they would be broken. The shakings were so strong that several objects on the vessel were thrown down. Everyone believed the ship had struck on rocks. The captain leaned over the taffrail in order to see the position of the reef, but soon saw that the vessel had struck nothing, and informed his crew "it was only an earthquake shock."

Another of the log books examined by Rudolph was that of a ship in the same part of the Atlantic Ocean. This record showed that suddenly on a morning, in 1883, strange noises were heard that soon increased and became not unlike the firing of great guns or the peals of distant thunder. The ship vibrated as if its anchor had been suddenly let go, and at the same time a feeling came over all the crew, as if they had been electrified.

In some cases the vibrations were sufficiently severe to throw heavy objects from the deck, as appears in an account given by a French geologist of a quake in the Mediterranean off the shores of Asia Minor.

"Our ship was over the epicentre,"[5] he says, "and was so severely shaken that at first the Admiral feared the complete destruction of the corvette." He then makes the statement that the shocks which were directly upwards were so strong as to throw heavy objects in the air; for example, a heavy gun and its carriage. While it is possible, as Dutton remarks, that this incident of the heavy gun and carriage was grossly exaggerated, yet it should not be forgotten that in the case of submarine eruptions such as that which resulted in the production of the island of Sabrina, an immense column of water, weighing probably many times more than a gun and its carriage, was observed to be shot high into the air.

Where the seaquake is produced by a strong submarine volcanic eruption, there is a violent commotion of the water itself, so that a vessel passing over such a point may be greatly injured, and, indeed, even destroyed. Such disasters, however, are fortunately exceedingly rare.