Lava rock

“ On the surface of the seething lava in the throat of the volcano there gathers a rock foam, which, when hurled into the air, is cooled and falls as PUMICE,—a spongy gray rock so light that it floats on water. ”

“ The place here where the Althing met was a most singular and convenient one. Except from six to twelve inches or more of soil on top, the earth here is solid rock that was once lava. There are two wide and deep seams or cracks in this lava-rock, that meet at an acute angle, and stretch away in different directions into the plain. Between these, in a small hollow, shaped like an amphitheater, is the place where the Althing met. These seams or chasms are like natural canals, from twenty to fifty feet wide, and said to be two hundred feet deep. ”

“ When we first came into the plain it was on the edge of the lava, sandy but grown over with willow and grass; we are on pure lava now, which is also far from barren, being much grown about with grass and willow, but chiefly birch; everywhere, however, the bare molten rock shows in places, never tossed up in waves, but always curdled like the cooling fire-stream it once was, and often these strands or curdles are twisted regularly like a rope. ”

“ The surface of ordinary lava-flows remains rough for centuries, and only slowly crumbles down before weathering to form a soil. While tuff-beds provide light and fertile lands, the lava-streams remain marked out among them, as sinuous bands of rock, given over to an irregular growth of woodland. ”

“ In many cases volcanoes themselves are left, though they may have been for ages extinct. In some volcanic regions where no great central cones have existed the vast floods of lava that were poured forth extend to-day as vast black plains of naked rock, mottled with shifting sand-hills, or as undulating tablelands carved by running water into valleys and ravines, between which the successive sheets of lava are exposed in terraced hills. ”

“ The column of lava rises, breaks through the side of the mountain, and discharges in lava streams. There are no explosions, and usually no earthquakes, or very slight ones, accompany the eruptions. The lava in the calderas boils because of escaping steam, but the vapor emitted is comparatively little, and seldom hangs above the summits in heavy clouds. We see here in its simplest form the most impressive and important fact in all volcanic action, molten rock has been driven upward to the surface from some deep-lying source.
Fig. 214. Pahoehoe Lava, Hawaii
Lava flows. ”

“ It is interesting thus to trace the steps by which a compact granular rock becomes converted into a vesicular, pseudo-porphyritic lava, and finally into red scoriæ. The structure and composition of the embedded fragments show that they are parts either of a mass of primary rock which has undergone considerable change from volcanic action, or more probably of the crust of a body of cooled and crystallised lava, which has afterwards been broken up and re-liquified; the crust being less acted on by the renewed heat and movement. ”

“ The descent down the cone is difficult, from its extreme rapidity, and from the fall of large stones, which loosen themselves from the beds of pumice. Having at last scrambled to the bottom, we pursued our march down the other course of the lava, that is to say, down its westerly side, having ascended its eastern. The ravines and rents in this stream of lava are deep and formidable; the descent into them is always painful and troublesome, often dangerous: in some places we let ourselves down from rock to rock. ”

“ The outside shell under oceans, and over three-quarters of the earth, is covered by basaltic lava, and wherever igneous rock has been formed by volcanic action, intrusive or extrusive black basic lava recurs as dikes and outflows. ”

“ On our way we crossed by a narrow bridge-like rock over a terrible chasm, deep, straight-sided, and with water at the bottom, into a little sunken plain nearly round, all grass-grown and smooth and flat, round which the lava has run without breaking into it: a small stream follows the inside of the lava wave nearly all round this strange place, and through its opening we ride into the lava again ”

“ And when in active operation, these great volcanic vents discharged such contents of molten rock that, overspreading the whole region, the lava flood from one mountain would meet a like flood from its opposite mountain at a halfway point between the two volcanoes. These slow moving rivers of lava, carrying on their frontal margin a d rift of
rubbish, rock and earth, would meet at the common center, but not coalesce. ”

“ A lava-current which entered a lake or the sea, however, has sometimes caught up much of the sediment gathering there, and become so commingled with it, that in some parts it is hard to say whether the resulting rock is more igneous or aqueous. Lava which has been squirted up from below into cracks and crevices, and there [Pg 71] consolidated so as to form dykes, sometimes, but not often, produces considerable alteration upon the rocks which it intersects. The basaltic structure is believed to be due to the contraction of lava consequent upon its cooling. ”

“ Let us further assume, but for a moment only, that the cohesion of the solid rocks of the crust does not impede the upward progress of the fluid rock, nor prevent it from spreading laterally at any level. The lava will then obey strictly the general law of hydrostatics, and assume the station which will give the lowest possible position to the center of gravity of the strata and lava combined.
(1) If the fluid rock is less dense than the solid, it will pass through it to the surface and build a subaërial mountain. ”

“ It consists of nine separate little streams of lava piled upon each other; and of an irregular pinnacle, about fifteen feet high, of reddish-brown, vesicular basalt, abounding with large crystals of glassy albite, and with fused augite. This pinnacle, and some adjoining paps of rock on the beach, represent the axis of the crater. The streams of lava can be followed up a little ravine, at right angles to the coast, for between ten and fifteen yards, where they are hidden by detritus: along the beach they are visible for nearly eighty yards, and I do not believe that they extend much further. ”

“ Igneous.—As the name denotes, igneous rocks have risen from the heated interior of the earth. In a modern volcano, lava ascends the central funnel, and, issuing from the lip of the crater or from lateral fissures, pours down the slopes of the cone in sheets of melted rock. The upper surface of the lava column within the volcano is kept in constant ebullition by the rise of steam through its mass. ”

“ There’s nothing like habit. Long practice may make sleeping on a solid rock go as well as a bed of down.
Rocks were piled on rocks, and deep and broad cracks and seams were seen at intervals. Across one chasm through which, deep in the earth, we could hear a stream of water running, was thrown a natural arch of lava, that served as a bridge where the road crosses. ”

“ The pipe of a volcano rises from far below the base of the cone,—from the deep reservoir from which its eruptions are supplied. When the volcano has become extinct this great tube remains filled with hardened lava. It forms a cylindrical core of solid rock, except for some distance below the ancient crater, where it may contain a mass of fragments which had fallen back into the chimney after being hurled into the air. ”

“ Lava is molten rock of excessively high temperature, which suddenly becomes released from the fearful pressures of earth's interior. Hurled from volcanic vents, or gushing from cracks in the earth's skin, it spreads rapidly over large neighborhoods, filling valleys and raising bulky rounded masses. ”

“ Immediately after the lowering, the liquid lava of Halemaumau welled up border wall cracks and cascaded through the talus to form an oval pool in the bottom funnel of broken rock. The lava column rose 600 feet in the next six months and a lobate lake developed, its coves separated by sectors of overflow lava which lifted slowly into crags in the center. ”

“ 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. ”

“ 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. ”

“ What a contrast between the wooded hillside adjoining, with its carpet of soft volcanic sand, and the jagged surface of the lava! Care must be taken in climbing over the lava, for the sharp points and angles are ever ready to tear one's shoes and hands. It cannot be many years since these hard, cold rocks formed a glowing mass of molten matter creeping quietly out of some hidden fissure which reached far down into the earth. The lava hardened as it became cold, just as does molten iron when led from the furnace to make a casting. ”

“ For miles around, the rocks were spouting steam, hissing and roaring, and filling the whole air with pent-up gases from the great laboratory beneath; while burning streams of red-hot lava came rolling onward in stern, irresistible waves, now plunging in majestic grandeur over a deep precipice, or sweeping away the vegetation of the earth and shrivelling up huge forest trees in its relentless, solemn fury. ”

“ Precipices rise at times two thousand feet, sheer as a wall. Elsewhere gentle slopes of powdery lava, moss-tinted, connect rim and water with a ruler line. And between these two extremes are found every fashion and kind and degree of lava wall, many of them precipitous, most of them rugged, all of them contorted and carved in the most fantastic manner that imagination can picture. Caves open their dark doors at water's edge. Towered rocks emerge from submerged reefs. A mimic volcano rises from the water near one side. Perpetual snow fills sheltered crevices in the southern rim. ”

“ For, a multitude of causes tend, near the land, to reduce the bottom of the sea to a nearly uniform level,—the sediment of rivers,—materials transported by the waves and currents of the sea from wasting cliffs,—showers of sand and scoriæ ejected by volcanos, and scattered by the wind and waves. When, therefore, lava is poured out on such a surface, it will spread far and wide in every direction in a liquid sheet, which may afterwards, when raised up, form the tabular capping of the land. ”

“ All of these buttes combined could not have made the overflow constituting the beds, albeit the lips of the craters have been cut by streams of lava which cooled in the shadowy past. The marvelous power of nature, as exemplified in the configuration of the rocks about these buttes, and the lines of demarkation between fusion complete and arrested, make a lasting impression upon the most superficial beholder. There is an appalling sublimity in the sight which one can not shake off. The surface of the earth is in ruins here. Tree, plant, and grass are absent. The lava is a sombre black. ”

“ Then from one and another volcanic cone—perhaps from fifty—will the glowing lava burst forth; red-hot stones will be driven furiously upward; vapor, and smoke, and flames will be poured out, and the dark and jagged sides of that vast furnace will glow with unearthly splendor; and here and there will lakes of liquid lava appear, one or two miles in extent, heaving up their billows, and dashing their fiery spray high into the air. O, there is not on earth a livelier emblem of the world of despair ”

“ To the mechanical energies which steam exerts at the base of the fiery funnel, and in the substance of the mass of lava, we may, perhaps, refer most of the phenomena attesting great expansive power. The ashes, scoriæ, and stones which are shot upwards from the mouth of the volcano, and fall in showers around, are of the same mineral composition as the solidified parts of the lava: they mostly rest on the slopes, and augment by external layers of growth the diameter of the volcanic mound. ”

“ It is difficult for one who has not seen it to picture to himself the scene that lay around us. Devastation every where; lava covering the whole region in heaps upon heaps, fantastically piled one on the other. Here a huge isolated mound rises, seemingly cut off on all sides from the lava around; there we see how a mighty stream once rushed down the mountain-side, and cooled gradually into stone. Immense chasms are filled with lava masses, which have lain here for many years cold and motionless, and will probably remain for as many more, for their fury has spent itself. ”

“ The sombre color of the lava from which it has risen again and again after being swallowed up by it, as if it had found the seeds of renewed life in its own ashes, after the manner of the phœnix, the open plain which surrounds it, and the cruel reefs of lava which have taken root in its harbor, as if to darken with their stern shadow even the shimmer of the waves—everything about the city is majestic and melancholy. ”