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been observed here. Some action of the sort is indeed represented sometimes, but only in a feeble way. Ordinarily the lava spouts forth in stupendous quantities, but as quietly as water from a fountain. So mild are the eruptive forces that the observer may stand to the windward of one of these fountains and so near it that the heat will make the face tingle, yet without danger. Usually the outbreak takes place without warning, and even without the knowledge of people in the vicinity, who first become aware of it at nightfall, when the heavens are aglow with the reflected light and the fiery fountains are seen playing. As the news spreads hundreds of people flock to witness the sublime spectacle, and display as much eagerness to approach the scene of an eruption as the people of other countries show to get away from one.
All this is in contrast with the ordinary volcano. At the other extreme is such an eruption as that which happened last August, at Krakatoa, in the Straits of Sunda. With the published details of this catastrophe you are all familiar. Appalling as it was, the eruption of Sumbawa in 1815 must have been, if can rely upon the accounts of it, even more energetic and destructive. The eruption of Coseguina, in Nicaragua, in 1835, appears to have been of the same character, or upon a scale quite equal; while once or twice in a century Cotapaxi shakes the chain of the Andes through half its length, fills the sky with dust, and converts noonday into midnight for a hundred miles around. The eruptions of Aetna have all been on a smaller scale, but still sufficient to fill all Sicily with terror. Vesuvius is usually regarded as an obstreperous vent, but its performauces are mere Fourth of July fireworks in comparison with these Day-of-Judgment proceedings at Sumbawa, Krakatoa, and Cotapaxi.
The explosive agent in these terrible convulsions is steam. In their original seat, miles deep in the earth, the lavas contain considerable quantities of water; but the condition of this water is such as we have, at the surface of the earth, no experience with, except as we observe it in volcanoes. It is water red hot, or even yellow hot, and under a pressure hundreds of times greater than that of the steam in a locomotive boiler—a pressure probably comparable to that exerted by gunpowder in a powerful cannon. Under the enormous pressure, occurring at a depth of several miles within the earth, water is absorbed by the lavas in much the same way as water itself absorbs ammonia gas, or as wine absorbs carbonic acid. When the lavas rise to the surface where the pressure is removed their explosive energy becomes terrible. The steam is given off as the uncorked bottle of wine gives off its gas, only a thousand times more violently and energetically. So densely charged with vapor of water are some lavas that when, as in the case of Krakatoa, a vent is found, the explosive energy becomes so great that the lava is blown into fine dust and dissipated in the surrounding atmosphere. Although this extreme of explosive activity is far too common for the comfort and safety of the human race it is by no means the most frequent. The more ordinary type of volcano is one in which the explosiveness is not so intense as to blow the whole of the ejected matter into impalpable dust, but blows it into pellets termed lapilli. These grains of lapilli are of all sizes, from that of a kernel of wheat up to those of cannon balls, and sometimes weigh a hundred tons or more. With a majority of volcanoes, whether active or extinct, the greater part of the material ejected is cast into the air in this fragmental form. Falling back around the orifice it builds up a fairly regular cone, with a cup on the summit. This is termed a cinder
cone. Most ot the volcanic piles of the world are crowned with cinder cones, the principal bulk of which consists of lapilli and scoriaceous lumps, with some massive portions of flowing lava streams mixed in. It is probable that quite half of the volcanic material now visible upon the globe consists of accumulations of such fragmental matter.
To this general method of extravasation Mauna Loa and Kilauea are remarkable exceptions. They consist almost wholly of massive sheets and floods of lava. On Mauna Loa there are but the most insignificant traces of fragmental products, and on Kilauea there are only a dozen or two of small cinder cones. The lavas of these great volcanoes flowed quietly out in enormous deluges, running sometimes for months, or even a whole year, with little or no explosive action throughout the entire duration of the flows.
One consequence of this quiet method of eruption has been to give to these colossal piles a wholly exceptional form among volcanoes. Instead of a huge cone crowning the apex of Mauna Loa, its summit is nearly a flat plain, 51/2 miles long and nearly 4 miles wide. Within this plain is sunken a pit 3 miles long, 2 miles wide, and 1,000 feet in depth. In the floor of this pit at certain times may be seen a lake of red-hot liquid lava, varying in size from time to time, but occasionally as large as 30 or 40 acres. At intervals of fifteen or twenty minutes a column of liquid lava of great brilliancy, as large and as high as the Washington monument will be when it is completed, is shot upward and falls back into the lava pool in a fiery spray. This grand display is sometimes kept up for months, and is generally terminated by an eruption. When an outbreak occurs it does not take place usually at the summit, but a fissure suddenly opens in the side of the mountain, out of which a sheet of lava spouts hundreds of feet into the air, and, falling, collects into a river of fire half a mile in width, and rushes at first with great velocity down the slope. After running some miles it reaches more level ground, where it spreads out in great lakes or fields. It also cools on the surface, which gradually freezes over. But it is still hot within, and beneath its hardened covering the liquid rivers are still running, and at the edges and along the front of the great sheet the limpid lava constantly breaks forth, pushing out fiery rivulets in advance and laterally.
These rivulets are shot out in quick succession here, there, and everywhere, gradually covering the ground by repeated offshoots. They soon blacken and harden, but only to be covered by another and another belch. The later progress of the stream is slow. When the lava first leaves the vent it may run 10 or 15 miles an hour. But later on the stream may advance less than 100 yards in a day. In November, 1880, a great eruption broke forth near the summit of Mauna Loa, and the ava poured out in heavy streams unceasingly for eleven months. There were three great streams flowing in as many directions, and the largest one extended from the vent a distance of nearly 50 miles. It reached the outskirts of the beautiful little town of Hilo, whose inhabitants had abandoned all hope that their village would escape, and had removed their portable property. But the flow stopped just at the edge of the village.
The massive and highly liquid character of the flows from Mauna Loa is the cause which has given this mountain its peculiar form. It is in contrast with all other volcanoes by virtue of its flat and gently sloped profiles. It ia a gently rising dome whose steeper slopes are only about 7 degrees, while its longer ones are only 4 degrees. Most volcanoes have slopes ranging all the way from 15 to 30 and even 40
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