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The volcanic island of Hawaii, the largest of the Sandwich Island chain, is situated in the mid Pacific, south of the Tropic of Cancer. As shown in Fig. 5, this island chain consists of Hawaii, Maui, Molokai, Oahu, Kauai, Nihau, and about eight large islands, together with numerous small islands, extending in a general northwest direction from Hawaii to Nihau, a distance of about 400 miles. Like most volcanic islands they lie in more or less straight lines, probably along fissures, in this case in two nearly parallel lines. The island of Nihau, however, is an exception, the direction of the greatest length being almost straight across the two parallel lines.

The Sandwich Islands lie 2,000 miles from San Francisco in deep water, between 2,000 and 3,000 fathoms, or between 12,000 and 18,000 feet in depth. This island chain consists of great volcanic mountains, that had, at one time, fifteen active volcanoes of the first class. These are now all extinct but three, and all of these are on the island of Hawaii.

In his report to the United States Geological Survey for 1882–83, Dutton states that the summit of Mt. Haleakala on East Maui is 10,350 feet above the sea level. Oahu has peaks on its eastern side 2,900 feet high, and peaks on the western side 3,850 feet high. The summit of Kauai is probably 6,200 feet above the sea.

Fig. 5. The Hawaiian Islands

From U. S. Geological Survey

It can be shown by deep-sea soundings that all these volcanic piles are the summits of a gigantic mountain mass that rises abruptly from the bed of the Pacific. There are reasons for believing that this submarine chain continues for many hundreds of miles in the same direction beyond Kauai.

The extinct volcano, Haleakala, on East Maui appears to have been in eruption at a much later day than Mt. Kea, which is also an extinct volcano. But the natives have no traditions of any eruptions.

The volcanoes on the other islands have been extinct for a very long time judging from the extent of their erosion. Dutton is of the opinion that the western islands of the chain have been extinct for much longer times than the remaining islands.

The Sandwich Islands, also known as the Hawaiian Islands, are one of the colonial possessions of the United States. The island of Hawaii is about 2,000 miles from San Francisco. Honolulu, on the island of Oahu, the principal seaport of the chain, has a pleasant climate, and is an important coaling station for warships, commercial vessels, whalers, and trading ships generally.

The principal product of the island is sugar cane.

The island of Hawaii, as shown in map, Fig. 6, consists of five volcanic mountains and some small coral reefs. These mountains are: Mt. Kea, on the north, 13,805 feet in height; Mt. Haulalai, in the west central part of the island, 8,273 feet in height; Mt. Loa, in the south central part of the island, 13,675 feet in height; Mt. Kilauea, twenty miles east of the crater of Loa, 4,040 feet high at the Volcano House, and 4,158 feet on the highest point on the west, and Kohala, 5,505 feet in height, running through the northwestern part of the island, and the Kohala mountains in the northwestern part.

Fig. 6. Hawaii

From Dana's Manual of Geology

Of these mountains, Mt. Loa and Kilauea are the only active volcanoes, and are in frequent eruption. Mt. Haulalai was in eruption during 1804. Mt. Kea has not been active during historical times, while Mt. Kohala has been inactive for so long a time that its slopes are deeply gullied wherever the rivers flow down them.

As you can see from the map, Hawaii is very large. It has a length of ninety-three miles from north to south, and a breadth of eighty miles from east to west, its area is about 6,500 square miles. With the exception of small patches of coral reefs, Hawaii is formed entirely of lava, and is the largest pile of lava in the world with the single exception of Iceland.

Where the islands of the Hawaiian chain have coral reefs extending off their coasts, excellent harbors are found in the deep waters between the islands and the reefs. Hawaii, however, has no extended reefs of this character, and, consequently, no first-class harbors. Hilo, on the eastern coast, is the best harbor, and is, therefore, the principal settlement.

A very brief examination of the map of Hawaii will show you that there are no rivers on the island, except on the sides exposed to the wind, that is, on the northern and northeastern slopes. Since the yearly rainfall on Hawaii is large, being in the neighborhood of a hundred inches, you will understand that considerable rain water falls on the island. In those parts of the island where it does not run off the surface it must drain downward through the loose piles of broken rocks or cinders. A rainfall of one hundred inches a year means that if all the rain which falls on each square foot of surface was collected in a flat vessel one foot square with vertical sides it would fill the vessel to the depth of one hundred inches, or over eight feet. The drainage of the rainwater downwards through these parts of the island, must, therefore, be large.

Another curious fact you can notice on the map, is that the lava streams of the past fifty years from Mt. Loa indicated by heavy dotted lines, in no cases begin at the crater, but start at fairly considerable distances from it. Later on in this chapter we shall explain the reason for this curious fact.

Since practically the whole of Hawaii has been formed from the streams of lava that have flowed at one time or another, you can understand how great these flows must have been. But to do this fully you must not only take into consideration the portions of the island that lie above the ocean and reach into the air at its greatest height to 13,805 feet above its surface, you must also remember that this mountain rises from a deep ocean, so that if all the water were removed, you would see Hawaii towering up above the former level of the sea to the height of about 31,000 feet, or higher than Mt. Everest, the highest point on the earth above the present sea level. This would be, approximately, five and eight-tenths miles. You can understand, therefore, how great the flow of lava must have been.

We shall begin the description of Hawaii with the active volcano of Mt. Loa, or, as it is sometimes called in Hawaii, "The White Mountain."

You will remember that the eruption of Krakatoa was of the explosive type. Practically no melted rock or lava escaped from the crater. Indeed, if it had escaped it would not have been seen; for, not only the cone near the crater, but also much of the mountain itself was blown completely out of sight and covered by the waters of the ocean.

The eruptions of Mt. Loa are of an entirely different type. In Loa there are no explosions, the eruptions being what are called the non-explosive or quiet volcanic eruption type. It will be necessary to explain some of the peculiarities of this kind of eruptions.

There is a great difference in the liquidity or the ease with which different kinds of lava flow. Some lava is very thick or viscid, or is sticky like thick molasses or tar, and therefore flows very sluggishly. Other lava is thin or mobile, more closely resembling water in the ease with which it flows. Now, in the case of a volcanic mountain of fairly considerable height, where the lava possesses marked liquidity, the lava as it rises from great depths in the tube of the volcano seldom flows over the top or rim of the crater. This is not because the force that brings the lava up is unable to carry it a few thousand feet higher, so that it can run over the brim of the crater, but because the walls of the volcanic mountains are unable to stand the great pressure which the mass of liquid lava exerts against their sides.

It can be shown that a column of liquid lava 500 feet high, will exert a pressure on the walls of the crater of about 625 pounds to the square inch. Therefore, in very high volcanic mountains, long before the lava can reach the edge of the crater and overflow, the pressure becomes so great, that cracks or fissures are made in the sides of the mountain, through which the lava is quietly discharged; when, of course, the level of the lava in the crater falls considerably. In volcanoes of the explosive type, no matter what may be the condition of lava, should a large quantity of water suddenly find an entrance to a large body of molten lava at some distance below the surface, the lava would be suddenly thrown explosively into the air, where being chilled, it would afterwards descend in showers of ashes, cinders, or volcanic dust.

In some volcanic mountains such as Mt. Loa, the crater, instead of being situated at the top of a conical pass of ashes or other material, consists of a pit-like depression, generally occupying a level tract or plain at the top of the mountain. This pit is known as a caldera, or caldron, or what you might, perhaps, call a huge kettle or boiler. The pit has more or less vertical sides that extend downwards for unknown depths to the place from which the lava comes. The vertical walls of the caldera are not, however, smooth, but exhibit numerous horizontal ledges, that mark places where portions of the floor of the caldera were situated at different times.

At the bottom of the large pit or caldera on the summit of Mt. Loa can be seen the level floor formed of hardened lava. This floor is surrounded by vertical walls on which can be seen the broken edges of the old lake bed.

Captain Dutton, in a paper on Hawaiian volcanoes, prepared for the United States Geological Survey, and published in its Fourth Annual Report for 1882–83, thus describes the appearance at the great crater as it was in 1882.

"The summit of Mauna Loa (Mt. Loa), is a broad and large platform about five miles in length and four miles in width, within which is sunken the great caldera called Mokuaweoweo. The distance from the point where we first reach the summit to the brink of the pit is about a mile and a half. The surface of the platform is much more rugged than the slopes just ascended. It is riven with cracks, and small faults,[2] and piles of shattered rock are seen on every hand. Nowhere is there to be seen the semblance of a cinder cone. Doubtless many eruptions have broken forth from the various fissures on this summit, but only here and there can insignificant traces of such catastrophes be definitely distinguished. The absence of fragmental ejecta (broken rock that are thrown out) is extraordinary. The shattered blocks, slabs, and spalls (chips) which everywhere cumber the surface appear to have resulted from the spontaneous shivering and shattering of the lava sheets by their own internal tensions as they cooled.

Fig. 7, taken from Dutton's report, gives the general shape of this great caldera. Dutton's description of the same is as follows:

"The length of the main caldera is a little less than three miles and its width about a mile and three-quarters. Its floor, viewed from above, appears to be composed of a series of flat surfaces occupying two distinct levels, the higher upon the surface of the black ledge, the lower lying within the ledge. Upon the western side is a small cinder cone standing close upon the border of the black ledge. It is the only one visible, either within the caldera or upon the surrounding summit. Its height is about 125 or 130 feet. It was seen in operation, throwing up steam, clots of lava, and lapilli (some of the larger pieces of fragmentary lava) in the year 1878. The only other diversifications of the floor are many cracks which traverse it, the larger of which are distinctly visible from above. Some of them are considerably faulted. There is no difficulty in recognizing the fact that the whole floor has been produced by the sinkage of the lava beds which once continued over the entire extent of the depression, their undersides having been melted off most probably by the fires beneath. The lava beds in the immediate vicinity of the brink upon the summit platform wear the aspect of some antiquity. They have become brown and carious by weathering, and, although no soil is generated, little drifts of gravel are seen here and there mixed with pumice. Since the caldera was formed there is no indication that the lavas have anywhere overflowed its rim. And yet it is a very strange fact that within a half mile, and again within a mile to a mile and a half, lavas have been repeatedly erupted within the last forty years from the summit platform, and have outflowed at points situated from 700 to 900 feet above the level of the lava lake within. Traces may also be seen, at varying distances back of the rim, of very many eruptions in which the rocks betoken great recency, although no dates can be assigned to their occurrence."

Fig. 7. Panorama of Mokuaweoweo

From U. S. Geological Survey

Fig. 8. View of the Crater of Kilauea from the Volcano House

From U. S. Geological Survey

During his visit to this great pit, Captain Dutton succeeded in climbing down the almost vertical walls on the side of the crater, and, reaching the surface of the hardened lake, walked over it. It must have required no little courage to thus venture on the thin floor of a lake which he knew was filled to great depths with red hot boiling lava, for he was walking over the surface of a slumbering volcano, that might at almost any moment awaken, and opening, swallow him and his companions. Through enormous cracks in the floor, he could feel the heat from the molten mass, while, through the same openings came suggestive whiffs of sulphur vapor.

During the eruption of this mountain, on January 23d, 1859, the light from the glowing lava streams was bright enough to read fine print at Hilo, a distance of thirty-five miles.

During the eruption of 1852, a stream of white-hot lava was thrown up into the air from one of the fissures to a height of from 300 to 400 feet.

Stones and Lava Thrown Upwards—Eruption of Mokuaweoweo, Hawaii, July 4–21, 1899

From a Stereograph, Copyright, by Underwood & Underwood

When an eruption takes place in Mt. Loa the column of lava slowly rises in the crater, threatening to overflow its lowest edges, but before this can take place the pressure becomes so great that some portion of the mountain below the crater is fractured and the lava quietly escapes.

During some conditions of the mountain every fifteen or twenty minutes a column of highly glowing lava is shot upwards like a fountain to a height of 500 feet and over, falling back into the lake in fiery spray. Unusual heights of these streams are generally followed by an eruption.

These curious jets of molten rock certainly cannot be due to the pressure of higher columns of lava, since the crater itself is near the top of a high plain. They are believed to be due to steam formed by the penetration of the rain water that falls on this part of the mountain.

You can now understand why the lava streams escaping from Mt. Loa as shown on the map, in Fig. 6, do not begin at the level of the crater; for the discharge of the lava does not take place over the rim of the crater, but through the cracks or fissures formed further down the sides of the mountains. It must not be supposed, however, that the fissures are limited to the sides of the mountain where they can be seen. They probably occur in many places below the surface of the water on some part of the bed of the ocean.

The crevices that are formed in this manner in the sides of the mountain vary greatly in size, some being so narrow that the lava scarcely flows through them at all but simply fills up the crevice, hardens on cooling, and mends the cracks in the mountains, in the way that a crack is mended in a piece of china by the use of glue or in a wall of masonry by mortar. Through the largest crevices or cracks, however, large lava streams may continue to flow often for several weeks, or even longer.

Sometimes, especially towards the close of the eruptive flow, the lava may escape disruptively, so that small cones are formed along the lines of the fissures. Cones of this character are called lateral cones, and in the case of a volcanic island, where the lava flows out below the level of the water, the lateral cones sometimes project above the water and form volcanic islands or dangerous shoals that impede navigation.

When the lava pours out of a crevice in the side of the mountain, a river of molten rock rushes down the slopes, at first like a torrent, but on reaching the more nearly level ground, it spreads out in great lava lakes or fields, the surface of which takes on the characteristic black appearance of basalt, a certain kind of glass, for the lavas of Mt. Loa are generally basaltic. After an eruption the hardened floor of lava in the caldera, being no longer supported by the liquid mass formerly below it, falls in, leaving a large cavity with only the edges of the old floor clinging to the sides of the pit.

It will be interesting to give a short account of some of the great lava streams that have been poured out at different times from Mt. Loa.

In the great eruption of August 11th, 1855, the lava escaped through fissures from two to thirty inches in width. Then, flowing in a continuous stream, it did not stop until it was within five miles of Hilo.

In the eruption of January 23d, 1859, the lava stream flowed towards the northwest on the east side of Haulalai, reaching the sea in eight days.

The eruption of March 27th, 1868, was characterized by severe earthquake shocks, one of which, occurring on the second of April, destroyed many houses and produced huge fissures in the earth. These shocks produced great earthquake waves that reached distant coasts.

Mt. Kilauea, lies at a lower level towards the east. This crater is situated at 4,040 feet above the level of the sea, and is nearly 6,000 feet below the caldera on the top of Mt. Loa.

Fig. 8, taken from the United States Geological Survey, Fourth Annual Report, for 1882–83, shows a view of Kilauea from the Volcano House. Dutton gives the following description of the appearance of Halemaumau, the pit crater or caldera of Kilauea.

"In front of us and right beneath our feet, over the crest of a nearly vertical wall, more than 700 feet below, is outspread the broad floor of the far-famed Kilauea. It is a pit about three and a half miles in length, and two and a half miles in width, nearly elliptical in plan and surrounded with cliffs, for the most part inaccessible to human foot, and varying in altitude from a little more than 300 feet to a little more than 700 feet. The altitude of the point on which we stand is about 4,200 feet above the sea. …

"The object upon which the attention is instantly fixed is a large chaotic pile of rocks, situated in the centre of the amphitheatre, rising to a height which by an eye estimate appears to be about 350 to 400 feet. From innumerable places in its mass volumes of steam are poured forth and borne away to the leeward by the trade wind. The color of the pile is intensely black. …

"Around it spreads out the slightly undulated floor of the amphitheatre, as black as midnight. To the left of the steaming pile is an opening in the floor of the crater, within which we behold the ruddy gleams of boiling lava. From numerous points in the surrounding floor clouds of steam issue forth and melt away in the steady flow of the wind. The vapors issue most copiously from an area situated to the right of the central pile, and in the southern portion of the amphitheatre. Desolation and horror reign supreme. The engirdling walls everywhere hedge it in. But upon their summits, and upon the receiving platform beyond, are all the wealth and luxuriance of tropical vegetation heightening the contrast of the desolation below. … "

Fig. 9. Crater of Kilauea

From Dana's Manual of Geology

Fig. 9 represents the pit-like crater of Kilauea as it appeared after the eruption of 1886. Here, as will be seen, there are several lakes of lava, the largest of which is known as Halemaumau. The eruption of 1886, like all the eruptions of Kilauea, consisted of the escape of the lava from an opening on the side of the mountain below the crater, and a sinking in of the hardened floor of the crater. The figure also shows the position of the New Lake that lies east of Halemaumau. The extent and appearance of each of these lakes are constantly changing, both as to height and area.

Dutton gives the following description of the appearance of the lake of lava, and some curious phenomena that occur on its surface. He is describing the general appearance of the pool of molten lava covered as it is with a hardened black crust: