With the mention of the Lago de Amatitlan it occurs to me that the so-called volcanic lakes of Central America deserve a short notice. I would not claim that there are not here genuine pit-craters filled with water and called lagos or lagunas. On the summit of many of the extinct volcanoes are craters filled with water, as Ipala and others, and as Agua was before the destruction of the crater-lip in 1541; while in San Salvador and Nicaragua are many lakes, usually of small extent, but sometimes so large as to mislead the casual observer as to their origin, though of undoubtedly volcanic nature. Of this last class is the Lago de Masaya, from whose deep pool the people of the neighboring village obtain all their water. Coatepeque is another volcanic lake, whose walls are so steep that they can be descended only at certain points by means of ladders and steps cut in the lava rock. Finally there are many pits, sometimes no more than a hundred feet in diameter, but of very great depth, and filled sometimes with fresh water, but more commonly with saline waters so strongly impregnated as to be undrinkable. The great lakes of Amatitlan and Atitlan are not certainly volcanic, although their shores are dotted with hot-springs and guarded by volcanoes,—they are not, that is, actual craters; but the former seems to be the result of a subsidence caused perhaps by the removal of material from lower layers by eruptions of Pacaya, and it is of no considerable depth, while good authority has considered the Lago de Atitlan the result of damming up a valley and streams by the masses of the volcanic group of the same name. A glance at the map of this lake (p. 154) as given by the French geologists whose opinion is quoted, will show that the volcanoes occupy a position not far from the geometrical centre of the Lago, or where they should be if the lake was an ancient crater. Compare with this, if you will, the plan of an undoubted volcanic lake, that of Ilopango in San Salvador. This body of water is not only the seat of volcanic eruptions, as is also the Great Lake of Nicaragua, but probably fills a depression that has been the result of the coalescence of several points of eruption. I have before me the interesting report to the Guatemaltecan Government by my friend Edwin Rockstroh of his observations made on the eruption of one of these craters in 1880. The lake is 9,200 metres wide from east to west, and 7,300 metres from north to south, with an area of 54.3 kilometres. Completely surrounded by precipitous mountains, interrupted only on the southeast by the narrow gorge through which the waters of the lake are discharged, it receives no important affluents from the surface; and as its emissary is of much greater volume at all seasons than these insignificant brooks, it is probably fed by subterranean springs,—indeed one of these, near the south shore, enters with such force as to cause a ripple on the surface of the lake. Soundings indicate a cup-like bottom with an extreme depth of less than seven hundred feet (209.26 metres). The level of the lake has often changed, and in 1880 the surface-level fell more than thirty-four feet, leaving exposed stumps of trees encrusted with calcareous deposits. It was before the last eruption well stocked with fish of the varieties called by the people who lived near by mojarra, burrito (both species of the genus Heros), pepesca, and chimbolo. At times an eruption of sulphurous gases partly asphyxiated the fish, driving them to the shores, where they fell a prey to the fishermen. What the fishermen did on occasion of greater disturbances is told in the following extract from a Guatemaltecan journal;[66] the author, Don Camillo Galvan, formerly Visitador-General, writes as follows:—

“The people of the pueblos around the lake, Cojutepeque, Texacuangos, and Tepezontes, say that when the earthquakes came from the lake, which they knew by the disappearance of fish, it was a sign that the monster lord of those regions who dwelt in the depths of the lake was eating the fish, and probably would consume them all shortly, unless provided with a more delicate and juicy diet worthy of his power and voracity; for they say that the monster only eats fish as men eat fruit, to refresh and allay hunger. The natives, deeply afflicted by the fish famine, the failure of an article of commerce and their ordinary diet, collected at the command of their chiefs. Then the sorcerers (los brujos) commanded the people to throw flowers and fruits into the lake: if the tremblings continued, they were to cast in animals, preferring conies (Lepus Douglassii), taltusas (Geomys heterodus), then armadillos (Dasypus), and mapachines (Procyon cancrivorus). These animals must be caught alive and cast living into the water, under penalty of no less than hanging with the vine zinak. If some days passed, and the tremors continued, and the fish did not come out of their caves, they (the brujos) took a girl of from six to nine years old, decked her with flowers, and at midnight the wizards took her to the middle of the lake and cast her in, bound hand and foot and with a stone fast to her neck. The next day, if the child appeared upon the surface and the tremors continued, another victim was cast into the lake with the same ceremonies.

“Even in the years 1861 and 1862, when I visited these towns, they told me, though with much reserve, that the people of Cojutepeque and Chinameca kept this barbarous custom to prevent the failure of the fish.”

Near the end of November, 1879, a series of earthquakes shook the lake (more than six hundred were counted), and on Jan. 11, 1880, the waters had risen about four feet. On the next day, between half-past four and half-past seven in the afternoon, 13,790,000 cubic metres of water escaped from the outlet of the lake, making a stream of greater volume than the Seine at Paris or the Rhine at Basle. The little river Jiboa, which received this torrent, did great damage to the plantations on its banks.

As is usual, the earthquakes were accompanied by the discharge of sulphuretted hydrogen, now in such quantities as to be very unpleasant at the city of San Salvador. On the 9th of January there appeared floating on the surface numerous flakes of a black foam composed of ferric sulphide, which in contact with flame burned with a slight explosion. On the 20th, at eleven o’clock in the evening, a great disturbance was noticed in the midst of the lake, and the next morning a pile of rocks was seen, from whose midst arose a column of vapor. For more than a month this vapor column was visible, and the pile of rocks near the centre of the lake increased, while the water was heated and the sulphurous vapors extended over all the neighborhood. Beyond this no permanent volcano was formed above the level of the lake (1,600 feet above the sea).

It is dangerous to form conclusions as to the general course of volcanic action anywhere, for science is very much in the dark as to the causes of eruptions and earthquakes, as to the condition of the interior of our globe, whether fluid or solid, and also as to whether the lavas poured out during an eruption have been fluid since the earth was formed, or have been suddenly melted either as cause or effect of what we call an eruption. In the Central American volcanic region, as was stated at the beginning of this chapter, little has been done in the way of scientific exploration, and the facts recorded, beyond popular accounts of some especial disturbance, are so meagre that no large space would be required to present them to the reader. This is not, however, the place to enter into a scientific discussion, and I must content myself with a few bare statements.

In the first place, the volcanoes of the country discharge both ashes and lava, the latter being most frequently trachytic. Basaltic lavas occur, though less frequently than in Mexico and farther northward; and the columnar structure seen so well at Regla in Mexico is very rare in Guatemala. On the other hand, pumice and obsidian, which are classed with the acid or trachytic lavas, are abundant, the latter furnishing material for knives, while the former has many applications in the arts of the present day. I have seen both basalt and basaltic rapilli in eastern Guatemala near the boundary of San Salvador, and basaltic sand is common on the southern coast.

Another feature of the Central American volcanoes is their remarkable regularity of form. This is due to the fact that the emissions consist of ash and lava of slight fluidity. In the Hawaiian Islands, where the basaltic lava is more fluid than in any other volcanic region, the lava-streams often flow for months, and extend fifty or sixty miles from the crater, building by successive eruptions a cone of great diameter in proportion to their height; Mauna Loa having a diameter of ninety miles at the sea-level, with a height of less than fourteen thousand feet and a slope of about seven degrees. The eruptions of the American volcanoes are mainly of masses of rock which are piled regularly about the base, in this way increasing the height, and great quantities of sand which fills the interstices, and finally of lava in a thick, viscid state which clings to the slopes of the growing cone and cements together the sand and larger fragments. No lava-stream, at least of modern times, has been found at any considerable distance from its source.

From the specimens I collected in some of the ravines which traverse the older deposits, I saw that in former ages the outflow was not only different from that of modern times, but of great variety of form in contemporaneous streams, although the chemical composition did not vary essentially.

Earthquakes are mainly due to the injection of intensely heated lava into strata of cold rock in the process of forming dikes. When a volcano pours its lava out of its summit-crater, the eruption may be wholly free from earth tremors, as is often the case on the Hawaiian Islands; and this gives rise to the popular belief that active volcanoes are in some way a safety-valve for the subterranean forces. When, however, the shrinkage of the earth’s crust or the explosive force of pent-up vapors cracks the solid rock, thus giving passage to the molten mass which must be supposed to underlie this volcanic region, the sudden contact of two bodies of very different temperatures (perhaps two thousand degrees) must cause vibrations entirely sufficient to account for the worst earthquake recorded. That the supply of molten rock is ample beneath the crust of this region, we have proof in the constant activity of Izalco, which for more than a century has poured out lava with the other ejections.

This theory of earthquake action is so simple that it must commend itself to any one who has observed the powerful vibrations excited by placing a cold kettle upon a hot stove, or by admitting with force a stream of hot water into a bath-tub partly filled with cold water. It may be stated also that lava is a remarkably poor conductor of heat (I have been able to walk over a crust that bent beneath my weight, and again where I left footprints in the half-hardened lava), and solid lava might retain a temperature of less than two hundred within a few feet of a molten mass ranging among the thousands of degrees. The secular refrigeration of the subterranean molten masses due to the slight conductivity of solid lava is well illustrated in the temperature of hot-springs, that remains unchanged for centuries.

Eruptions are usually of an explosive nature in the Central American region (as described in the outbreak of Coseguina), and the ejected ash is scattered often to a great distance to form by its decomposition layers of soil especially fitted for the cultivation of coffee, sugar, and the vine. Sulphur is not so abundantly deposited as at Ætna, Hekla, or even the Mexican volcanoes.