The physics of fire: Why some volcanoes pour lava and others explode

“ The law of the land enjoins us to use them in such manner that they may be passed unimpaired for the enjoyment of future generations.
The story of HAWAII NATIONAL PARK is the story of active volcanism singularly marked by eruptions of very fluent lava. The park is in two sections; that on the island of Maui, discussed in this guide, includes the great eroded crater of Haleakala Volcano; that on the island of Hawaii embraces the summits of Mauna Loa and Kilauea Volcanoes. ”

“ Sometimes these fires burst forth from the crater of the volcano with tremendous force. The smoke becomes thick and black, and lurid flames shoot up to a height of hundreds of feet, making a scene of amazing grandeur.
With the flames there are thrown out stones, ashes, and streams of melted rock, called lava. This lava flows down the sides of the mountain, and, being red-hot, destroys every thing with which it comes in contact. At such times, a volcano is said to be in eruption. ”

“ Take a film about the volcano, of which most children have heard but never seen. It would explain that a volcano throws up smoke, calcined dust, red-hot stones, and melted matter called lava. The summit is hollowed out in a great excavation having [33] the shape of a funnel, sometimes miles in circumference. The principal volcanoes could be shown, as Vesuvius, near Naples; Etna, in Sicily; Hecla, in Iceland.
A curtain of smoke filling the orifice of the crater denotes the forthcoming eruption. ”

“ By the study of volcanoes and their products we learn that the fused substances are not everywhere precisely the same and do not remain absolutely uniform, even in the same volcanic region. But in what manner and from what causes these variations arise is still unknown. We are further aware that the molten magma, under a centre of volcanic disturbance, manifests from time to time energetic movements which culminate in eruptions at the surface. ”

“ From this volcano Kilauea, and the crater Mokuaweoweo, which lies like an island in the top of Mauna Loa, nearly 10,000 feet higher, come enormous and sometimes destructive lava flows. They are called rivers of lava, but a lava river, unlike a stream of water, flows underneath a continually cooling and hardening crumpled surface, pushing its way from under and at last leaving long tunnels. Sometimes new lava melts through the walls of these caves and pours along the path left ages before, frequently finding an outlet even under the waves of the sea. ”

“ We have already seen that when an explosive volcanic eruption occurs there is suddenly thrown out of the crater of the volcano a huge column of various substances [Pg 181] that rises sometimes as high as 30,000 feet or even more. The smaller fragments of lava are quickly cooled and form volcanic ashes, sand, cinders, or dust. These are rapidly spread out by the wind in the form of a black cloud, that not only covers the mountain but reaches out over the surrounding country, completely shutting off the light of the sun. ”

“ In consequence of the peculiar constitution of the magma, the order in which minerals separate and solidify from it on cooling does not necessarily correspond with the inverse order of their relative fusibility. The lava differs from the magma before eruption, inasmuch as water and various volatile substances may be expelled on extrusion. The rapid escape of vapour from the lava contributes to the explosive phenomena of an eruption, whilst the rate at which the vapour is disengaged depends largely on the viscosity of the magma. ”

“ The emission is not usually accompanied, however, by violent explosions, such as are often associated with the eruption of magmas of less basic and more viscous nature. The viscosity of the lava at Kilauea was estimated by G. F. Becker to be about fifty times as great as that of water. It may be pointed out that the fusibility of a lava depends not on the mere fact that it is basic, but rather on the character of the bases. A lava from Etna or Vesuvius may be really as basic as one from Hawaii. ”

“ The "beams" of his eyes will kill a man. The dragon is found chiefly in India and Ethiopia. "His wings will carry him to seek his prey when and where occasion serveth"; his teeth are very sharp and set like a saw, but his prodigious strength "resteth in his tail." The amphisbena has two heads and no tail, "having a head at both ends." Africa "aboundeth" with them.
Volcanic Lava-Cones.—Professor Dana observes, in connection with studies of the recent eruption of Kilauea, that in external dress the crater of highly viscid lava is very unlike that of the feebly viscid. ”

“ Kilauea is more than two hundred miles southeast of Honolulu, and thirty miles inland from the port of Hilo. Twenty miles to the west from Kilauea is Mauna Loa. The crater of Haleakala is on a different island from Kilauea and Mauna Loa, about midway between these and Honolulu.
The active rim of Kilauea is four thousand feet above the sea. The slopes of [Pg 223] this volcano have an exceedingly flat grade. It is the most continuously active of the three volcanoes in this Park. It has a pit in which the molten lava rises and falls and is boiling all the time. ”

“ Few places on Earth allow closer or more dramatic views of volcanic activity than Mauna Loa and Kilauea volcanoes on the island of Hawaii. Their frequent but usually non-explosive eruptions make them ideal for scientific study. Kilauea’s eruptions are so intensely monitored that scientists have assembled a detailed picture of the volcano’s magma reservoir “plumbing” system and how it behaves before and during eruptions. ”

“ We others were influenced by field ambition, and since 1899 I had fought for a Hawaii geological survey, for I was convinced that Kilauea Volcano there must have an American volcano observatory.
My experiments on erosion, sedimentation, deformation, and eruption convinced me that a field experimental science was bound to grow up in each of those parts of dynamical geology. All of these needed field observatories to determine index of erosion, index of sedimentation, index of ground movement and earthquake, index of volcanism ”

“ The gentle fluctuations of lava in a crater while in a state of moderate activity are nowhere exhibited on a grander scale than in the pit of Kilauea on Mauna Loa. The mountain rises so gradually as almost to resemble a plain, and the crater appears like a vast gulf excavated in its flanks. The traveller perceives his approach to it by a few small clouds of steam, rising from fissures not far from his path. ”

“ In the centre was the still glowing stream of dark red lava, flowing slowly towards us, and in every direction were red-hot Page 265patches, and flames and smoke issuing from the ground. A bit of the 'black country' at night, with all the coal-heaps on fire, would give you some idea of the scene. Yet the first sensation is rather one of disappointment, as one expects greater activity on the part of the volcano; but the new crater was still to be seen, containing the lake of fire, with steep walls rising up in the midst of the sea of lava. ”

“ The fire-rock, breaking through the floor of the ocean to form the Hawaiian chain of islands, lost its power first in the far northwest and cooled and hardened from island to island until it is now making its last appearance on the largest and most southeasterly of all the group, the island known by the name Hawaii. Here is still to be found what is called the largest active crater in the world, Kilauea, and the sister crater, Mokuaweoweo, from which come the most voluminous lava flows, the latest one being in May, 1916. ”

“ We find there the largest extinct crater in the world. The great dead crater of Haleakala, in East Maui, is thirty miles in circumference. The crater of Kilauea, on the flank of Mauna Loa, is about seven miles in circumference. Several great eruptions have occurred in these islands during the past fifty years; and in one of these convulsions the volume of lava poured out was at least equal to the great outburst of Skaptar Jokul in Iceland. And when we consider the frequent recurrence of the Hawaiian eruptions, it at once appears that in this region lies the greatest lava producer on the globe. ”

“ In the same way volcanic action by the outpouring of lava through cracks is a process of solution of the deeper crust of the earth by hot gases, largely burning hydrogen. Lavas emerging from Etna or Mauna Loa are melted earth crust, dissolved and brought up by this same hydrogen and by other gases from the walls of profound cracks leading down to the earth core. Volcanism and metamorphism are thus the same process, namely the action of gases up cracks through deep earth crust. ”

“ The powerful agency of steam or aqueous vapor in volcanic eruptions leads us to compare its power of propelling lava to the surface with that which it exerts in driving up water in the pipe of an Icelandic geyser. Various gases also, rendered liquid by pressure at great depths, may aid in causing volcanic outbursts and in fissuring and convulsing the rocks during earthquakes. ”

“ It now appears that liquid lava is a gas froth, that Kilauea and Mauna Loa are all one system, that hydrogen is the most elemental gas in eruption, that a gas-free paste is the residue of flowing foam both in pits and lava flows, that earthquakes and vibrations are a function of this paste wedging up cracks and sinking back underground, and that the rise and fall is in tides and cycles, short and long. These things are not guesses, but measurements.
The earthquake problem at volcanoes is misunderstood in geology. The superstition that volcanic quakes are small is wrong. ”

“ Peak's eruption of a thousand cubic yards of lava in a few hours thrills us more than the Mississippi's erosion of an average foot of her vast valley in a hundred thousand years; yet the latter is enormously the greater. The explosion of Mount Katmai, the rise and fall of Kilauea's boiling lava, the playing of Yellowstone's monster geysers, the spectacle of Mazama's lake-filled crater, the steaming of the Cascade's myriad bubbling springs, all make strong appeal to the imagination. They carry home the realization of mysterious, overwhelming power. ”

“ Groundwater exists in large volume under all three volcanoes. Soufrière, Pelée and Vesuvius all began the steamblasts with collapsing craters, that is, with internal lava going down into the bowels of the earth. The lava usually showed in Vesuvius, whereas at Pelée and Soufrière it merely made fumaroles, or gas vents. Man, a mere microbe, could make nothing of hot sulfurous cracks. ”

“ The tourist who visits Mount Vesuvius at the time of a light eruption may thrust his staff into the stream of lava and extract a portion of the viscous substance in which are seen beautiful white crystals of the mineral leucite, each bounded by twenty-four crystal faces. It is clear that these crystals must have developed by a slow growth within the magma while it was still below the surface, and when the inclosing lava has consolidated, these earlier crystals lie scattered within a groundmass of glassy or minutely crystalline material. ”

“ On sloping surfaces it is found that the cellular cavities, common to lava which is cooled in the air, are elongated in a direction parallel to the slopes,—an effect clearly intelligible by considering the viscidity of the moving mass, and easily imitable by art. ”

“ The force by which mountains are elevated being the elasticity of the vapor diffused through the subjacent lava, it may happen, if the lava have a high degree of fluidity, that this vapor will collect in large masses, and rise as far as the lava is in a fluid state. The irregular [142] flow of lava from craters during an eruption is undoubtedly due to the rapid ascent of such steam bubbles through the lava. Such an accumulation of vapor under a mountain mass, if it cannot escape, would support it as long as the temperature remained unchanged. ”

“ But our chief danger was still in store for us; for just as we had arrived directly under the impending summit, as it were, a fearful explosion took place, and threatened to [Pg 107] ingulf us all in ruin. The crater of the volcano, which previously had only belched forth ashes and lava, now sent up high into the heavens a sheet of lurid fire. It did not resemble gases in combustion, which we denominate flame, flickering for a moment in transitory splendor, and then dying out forever. ”

“ When the mud dries it becomes hard and holds its shape, so that the sides of the gullies remain vertical, as they are cut by the streams, and do not crumble away as would softer soil.
Lava all blown to fragments We were very much surprised at the character of the ejecta close to the crater. Post-cards are current in Alaska showing great rocks which are said to have been “hurled from the volcano,” and we ourselves had expected to find something of the sort. ”

“ It may be argued that a miniature volcano erupts faster than a big volcanic system, but not if the whole terrestrial plexus of systems is taken into account. An eruption of Mauna Loa is a very slow affair, in comparison with the 10,000 underground squirtings of lava in cracks totally unperceived, except as tremors on seismograph.
Pelée’s eruption was like turning on a hose. A structural valve or orifice, suddenly opened by underground heaving of the mountain block and letting out steam and mud, appears to be the only reasonable explanation of what happened. ”

“ In the fall of rain and the flow of rivers, in the bubble of springs and the silence of frost, in the quiet creep of glaciers and the tumultuous rush of ocean-waves, in the tremor of the earthquake and the outburst of the volcano, we may recognize the same play of terrestrial forces by which the framework of the continents has been step by step evolved. ”

“ From these facts geologists have been led to the conclusion which we have already enunciated—namely, that the subterranean forces are in a state of continual flux over the surface of the globe. At one point of the earth's crust these forces gradually gather such energy as to rend asunder the superincumbent rock-masses and make themselves manifest at the surface in the series of phenomena characteristic of volcanic action. ”

“ From the intimate and complicated manner in which the elevatory and eruptive forces were shown to be connected during this train of phenomena, we may confidently come to the conclusion that the forces which slowly and by little starts uplift continents, and those which at successive periods pour forth volcanic matter from open orifices, are identical. From many reasons, I believe that the frequent quakings of the earth on this line of coast are caused by the rending of the strata, necessarily consequent on the tension of the land when upraised, and their injection by fluidified rock. ”

“ The metamorphism produced upon fragments of different kinds of foreign material enclosed within various igneous rocks has in recent years been studied in great detail by Professor Lacroix—Les Enclaves des Roches Volcaniques, Macon, 1893.
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It is not easy to comprehend the conditions under which large masses of molten material have been injected into the crust of the earth. The two main factors in volcanic action—terrestrial contraction and the energy of the vapours in the magma—have no doubt played the chief part in the process. ”

“ And it is only by such studies as these that we at last learn to regard the earthquake and volcanic phenomena of our globe, not as the grandest and most important effects of these forces, but as their secondary and accidental accompaniments. 'Volcanoes,' it has been said, 'are the safety-valves of the globe;' and when we come to realise the real extent and nature of the internal forces ceaselessly working in the earth's crust we shall scarcely be disposed to regard the simile as an overstrained one. ”

“ Instead, volcanoes are built by the accumulation of their own eruptive products—lava, bombs (crusted over lava blobs) , ashflows, and tephra (airborne ash and dust) . A volcano is most commonly a conical hill or mountain built around a vent that connects with reservoirs of molten rock below the surface of the Earth. The term volcano also refers to the opening or vent through which the molten rock and associated gases are expelled.
Fountaining lava and volcanic debris during the 1959 Kilauea Iki eruption of Kilauea Volcano, Hawaii. ”

“ How gaseous is lava? how radioactive is it? how often does it erupt? and how dangerous is it for human beings? With reference to the source, crack or crater, we need knowledge of how the earth crust is ruptured, how deep are the fractures, and how [89] much accompanied by earthquake is the wedging upward of lava in those cracks.
My first job on arriving in Hawaii was to make contact with Mr. Thurston and his associates. The next was to get a good map made of Kilauea Volcano as a basis for measurement of changes in the fire pit. ”

“ The third general fact is the repetitive nature of volcanic eruptions. A single outbreak with none following is an exceedingly rare phenomenon. Many eruptions, going often into the thousands, occur before the climax is reached and the decline of activity follows. The reason why a volcano, when its vent is once open, does not discharge all the material in its reservoir in one stupendous belch and then close up forever will be shortly brought up. ”