VOLCANOES

Dominion, Volume 22, Issue 92, 12 January 1929, Page 25

VOLCANOES

WHERE THEIR HEAT COMES FROM

HOW THE EARTH WAS FORMED

The eminent geologist, the late Professor T. G. Bonney, concluded Ills book on “Volcanoes,” published in 1902, with the paragraph: “Those among us who live to see the twentyfifth year of the present century are likely to be much wiser than we are now, for by that time many mists should have vanished and difficulties been surmounted.” His prophecy has proved truer than might have been expected, for a substantially new theory of volcanic action was expounded by the American geophysicist A L. Day, about the year 1925. The traditional theories of volcanic action have been distinctly tinged by medieval theology, which imagined volcanoes as hell’s vents. Given hell, then what more likely than that volcanoes were the occasional reminders of its eternal existence? Volcanoes have a sufficiently sinister aspect. J. A. Symonds describes Etna as “a most hideous place, like a pit in Dante’s hell, disused, for some unexplained reason, and left untenanted by fiends.” Though hell is no longer believed to be inside the earth, the idea has bequeathed an ideological ghost, for even scientists have been predisposed to imagine the inside of the eartli in a fiery, molten, tumultuously infernal state. This conception was destroyed by tidal and earthquake investigations, which proved that the earth is very rigid, even if very hot inside. When the idea of the molten interior had been banished, geologists invoked a deep molten or viscous layer, whose substance exuded through cracks in weak parts of the earth’s crust, forming volcanoes. The volcano was conceived essentially as a relatively mild and isolated offspring of a deep-seated world-wide activity. Hot and furious as volcanoes might be, they were as nothing to the reservoir of heat and fury from which they sprang.

New Theories of the Earth’s Interior. This conception of volcanoes as leaks has been clearly combated by Day. He collected the gases bubbling from the laval lake in the crater of Kilauea in Hawaii, and found them to be a highly reactive mixture; that is, the various gases in the mixture were from their nature vigorously interacting' and producing heat. Hence the lava was probably being heated by the interacting gases,. and th e interactions would be most advanced by the time the gases reached the lava’s surface. Thus the surface of the lava would be hotter than its depths. To test the deduction an iron tube containing suitable thermometers was thrust into the lava, and it was found that the temperature 20 feet below the surface was 100 deg. C. below the surface temperature. The volcano seemed to be standing on its head, as it were. Suddenly the revolutionary notion was conceived that perhaps, after all, we do see the worst of volcanoes, their maximum heat and fury occurring on the earth’s' surface as a relatively superfi-

cial phenomenon, and that they are not safety valves, ensuring the stability of a molten interior.

It is evident, according to this theory, that the escaping gases are the chief motive in volcanic action. Where do the gases come from? This is suggested by theories of the evolution of the earth. One of the most recent and best received is Dr. H. Jeffreys’s. He follows Laplace and others in conceiving the earth as a condensation in a strip of material pulled off the sun by a passing star. The portion forming the earth first cooled from gas to liquid. Later a crust formed on the liquid surface, which soon broke in pieces and sank to the earth’s centre. This process continued until the earth developed a honeycomb structure of solid lumps interspersed with liquid. In this way Dr. Jeffreys brilliantly accounts for the earth’s rigidity. As cooling proceeded many of these liquid inclusions more or less solidified, but still remained hotter than the surrounding lumps which had been cooled on the earth’s surface before foundering. Thus it is . not surprising that large volumes of extra hot material should occasionally be found iu odd places on the earth. In fact, it is reasonable to expect that any exceptional strain in the earth’s crust should open cracks between the surface and the nearest hot spots. Ocean boards and sea coasts and other places of abrupt change in surface structure would naturally have such cracks, and it is well known that these are the regions containing most volcanoes. Origin of Volcanic Gases. We have got more or less satisfactory arguments for the existence of hot spots of solid or even liquid material with cracks connecting them to the earth’s surface. Our next requirement is volumes of gas that escape from the hot spots up the cracks. These can be provided very nicely. It must be remembered that in the beginning the world was gaseous, and then an extremely hot liquid surrounded by a vast atmosphere of many hot gases. The hot liquid would , dissolve much gas, and in particular much water. This can be provide experimentally in the laboratory. Melted basalt rock proved a surprisingly good solvent of steam and other gases. Once dissolved in the earth’s interior material, the gases would not be able to escape owing to the pressure of the superincumbent layers. Thus the hot basalt substratum and inclusions in the earth are a vast reservoir of dissolved steam and gas. Any crack or earth movement reducing the pressure will immediately act as a conduit of steam and gases from the basalt to the surface. A volcanic area may now be conceived as honeycombed with cracks connecting different hot basalt inclusions with a few main vents in the earth’s surface. The different inclusions will in general deliver rather different gases, which will mix together in the main vents, with fierce chemical interaction, like the mixture of gases fed to a blast furnace. The fierce heat due the the chemical reactions will melt the neighbouring basalt, raising it to a much higher temperature than the greater masses of basalt below. The comparatively small quantity of basalt so liquified may flow over the sides of a main vent as a lava-flow. Vulcan’s Smithy. According to this theory, the volcano is very much like a blacksmith’s fire, or a blast-furnace. Indeed, in

Kilauea in Hawaii the crater bottom has been observed on occasion and seen to be cold. Several holes in the sides of the crater deliver blasts of gas which keep the lava molten over the ancient floor. Thus the volcano turns out to be much more Vulcanic than is generally believed. The intermittence of volcanic eruption can be ascribed to crystallisation, among other causes. As the basalt .n one of the liquid inclusions cools, it may actually reach a lower temperature than the normal solidifying point, an example of the phenomenon of super-cooling mentioned in a recent article in the “Manchester Guardian” on the freezing of meat. It is then liable to crystallise rapidly, As it crystallises, the dissolved steam and gas is rapidly evolved, producing temporary strong blasts through the cracks, and so the volcanic furnace is started. Since the whole earth is cooling steadily, special evolutions of gases from passing crystallisations may be expected at fairly regular intervals. The briefest outline of Dr. Day’s theory shows how radically the usual idea of volcanic action has been changed. It shows also how the subtle thread of one scientific principle may run through phenomena so apparently different as the production of glass, of good frozen beef, and of intermittence in volcanic eruptions.—“ Manchester Guardian.” TO SAVE AND SHAVE. Gone are the days when you were forced to buy new razor blades every few weeks —Durham Duplex blades have ended all that. Hollow ground and double-edged, these big chaps stand up stoutly to being stropped for months —sometimes years. Buy a Durham-Du-plex. Hardware shops and tobacconists.—Advt.