Into the Crater of a Volcano
Into the Crater of a Volcano
By CLEVELAND MOFFETT
Author of "Careers of Danger and Daring," etc.
DURING the summer of 1912 an important piece of scientific work, and one not lacking m adventure, was undertaken by Dr. Arthur L. Day, director of the geophysical laboratory of the Carnegie Institution, and his associate. Dr. E. S. Shepherd, in the course of which these two Americans made several, descents into the crater of Kilauea, the famous Hawaiian volcano, then in active eruption. The chief purpose of these difficult and dangerous descents was to obtain evidence bearing on the question whether water exists naturally in the hot interior of volcanoes, regardless of outside sources on the earth's surface, or whether this water, which has always been supposed to exist in volcanoes, leaks or filters in from rains, lakes, rivers, or oceans. The settling of this point would throw new light on the mechanism of volcanic eruptions, the mysterious causes of terrestrial disturbances, for the explosive force of steam is known to play an important part in them. But where does this steam come from?
In the hope of settling this question, the scientists purposed to study the gases thrown off by Kilauea, to analyze them, and learn what secret of the earth's constitution might be here revealed; but if this analysis was to have any special value, the gases must be studied inside the volcano, and not after the outside air, with its devouring oxygen, has combined with them and given them new chemical and physical characteristics. In other words, the gases must be secured before they had issued from the molten lake and suffered atmospheric contamination.
But how could this be done? How could these virgin gases be captured? What manner of gas-collector could be set up in the hot, poisonous crater two hundred feet below the rim? What metal would withstand the heat? Platinum, possibly, but platinum would let hydrogen filter through it, and would itself be eaten up by sulphur fumes. No wonder this problem of drawing off gases from a volcano's heart had never been solved. Even now it might not have been solved, as we shall see, but for a fortunate accident.
While waiting for some inspiration about a gas-collector, the Americans resolved to see if they could descend into Kilauea's crater, for their gas-collector would be of small service unless they could get near enough to the molten lava to operate it. So the immediate question was. Could they go down into this active volcano? And if so. Could they get up again?
The month of May, 1912, was drawing to a close, and every day saw Kilauea stirred to greater activity, as happens at the approach of her solstice periods. Ceaselessly white sulphur clouds hung over the vast fifteen-hundred-foot bowl of the crater, while up from the depths came a hissing and a roaring like the steam discharge from a dozen locomotives. Looking over the rim down the reddish brown sides of the bowl, one saw yellow fire fountains, fifty or sixty feet high, spurting up far below out of a splashing, sputtering lava lake, fire-colored, that opened to a width of a hundred yards and a length of two hundred yards in the black lava floor. From time to time lava rocks, loosened by the heat, crashed down upon this floor, while over it gushed floods of lava from the central fire well. These overflows of molten rock cooled quickly, layer on layer, from white heat to yellow, from yellow to red, from red to black, while through fissures in the surface layer the dull red glowed angrily beneath. One could look down into the smoking crater, especially at night, and see fantastic, fiery shapes, animals of fire, huge yellow serpents, with red eyes and flaming backs, writhing in the pit.
Dr. Day made the first attempt alone, starting early on a pleasant May morning and selecting for his descent a point on the eastern rim of the crater where the sun's long slant would keep him in the shade. He knew that he must end his labors before midday, because at that hour the sun would be directly overhead, and would send its tropical heat straight down into the crater. As long as he was in the shade, the air was cool enough, for a ten-mile trade-wind was blowing from the northeast. If his point of descent had been on the northeastern side, he would have had the purifying wind exactly at his back, which would have driven away deadly gases; but he would have much shortened the time in which he could work in the shade.
The chief danger was from volcano gases, especially sulphur fumes, that might be blown toward him and strangle him. A slight shifting of the wind of no more than ten degrees was enough to start a rotary motion of crater gases around the steep sides of the bowl, and if this motion continued, it would fare ill with a man down below, who would not be able to reach the surface. It should be understood that the sides of Kilauea's crater below the rim go down for a hundred feet in sheer perpendicular, so that it is a matter of slow and perilous mountain-climbing to go down or up.
For five hours on that memorable morning the American worked his way down the face of the precipice, moving cautiously from ledge to ledge, from one foot-hold to another, and, where there was none, breaking away the soft rock with his sharp-pointed hammer and a two-foot iron bar until he had a place to stand on. A dangling rope knotted to his belt and anchored securely above gave him a measure of safety, and he wore, fastened around his head and covering his nostrils, a sponge soaked in water from a small canteen. This sponge absorbed sulphurous fumes that he must otherwise have breathed. It was "a dirty and a dusty job," to use Dr. Day's brief description, but he finally accomplished it, and succeeded in blazing a trail down to the lava floor.
Happily, there was no misadventure on this occasion; the trade-wind blew unshiftingly, and Dr. Day suffered only moderate inconvenience from the gases. Strange to say, he found the air purer at the level of the lava lake than half-way down, due to the fact that the arriving trade-wind, cooler than the ascending gases, sank at once to the bottom of the crater and replaced them.
An interesting discovery made by the explorer when he reached the floor of the crater was that here the violent sounds of the volcano are hushed to a startling silence. The roaring and hissing that make so great a din overhead are scarcely heard below, the explanation being that the bowl-shaped crater multiplies the sounds as they ascend with increasing reverberations.
"Where was your companion while you were down at the bottom?" I asked.
"Guarding the rope."
"Did you call to him from below?"
"No. He could not have heard me for the noise of the volcano."
Now, as if in encouragement of this enterprise, the volcano itself proceeded to build the gas-collector desired by the geophysicists—a gas-collector made of ideal material; namely, the lava itself. Quite unexpectedly there gushed up in the black floor a fountain of lava, and as the splashes of this fountain cooled, they formed a circular wall that rose higher and higher with each fresh gush of lava, until presently the top, choking and narrowing like an Eskimo's snow house, closed over completely, and stood there a twelve-foot mound of lava, out of which streams of blue burning gases were seen to be escaping under high pressure from within. Here was the very thing they had been seeking, a natural collector and container of gases from the depths of the earth—gases that had never suffered air contamination. It remained only to draw off these precious gases by tapping the lava mound.
This they proceeded to do on May 28, 191 2, when four men made the descent: Dr. Day; Dr. Shepherd; Mr. Dodge, an assistant in the Kilauea research laboratory; and a native, an active little fellow who could climb like a monkey. Again all went well. The gas-collecting outfit, consisting of twenty glass tubes and tube connections, a piston pump and a long elbow of iron pipe to penetrate the lava mound, was lowered, together with two cameras with plates and tripods. It was 7 a.m. when the party reached the floor of the crater, and they stayed there about four hours.
"How thick was the floor of the crater?" I asked Dr. Day.
"The thickness varied," he explained. "We walked over lava in some places where the crust was a foot thick and in other places where it was only a few inches thick. The lava cools very quickly, and then breaks into cracks. Through these cracks we could see red fire underneath."
"Was n't it very hot?" I asked.
"We wore heavy boots, and the soles were scorched when we went near the edge of the molten lake. Sometimes we had to climb up on high rocks and let our boots cool off. But that was n't the most disagreeable part of our adventure. What really gave us trouble was the air we had to breathe. Despite our sponges, the sulphur fumes would catch us in the throat, and sometimes it seemed as if we were suffocating. We could get relief by bending close to the lava floor, where the air was better."
"Was there dense smoke over the molten lake?"
He shook his head.
"There was no smoke; the air is quite transparent over the hottest part of the lake except for the shimmer of heat. It is so hot that the gases are completely burned. However, you see smoke rising from the solid lava surrounding the lake, where the heat is not great enough to burn the gases. These come hissing up through fissures in the rocks, especially along the raised rim of lava that surrounds the lake. The hot flood undercuts this rim into caves of lava, just as the ocean digs out sand caves, and here the volcano gases accumulate under pressure, and rush out violently in white clouds."
"Do birds ever fly over an active crater?" I asked.
"Indeed they do. We saw miner-birds, a sort of awkward robin, darting and diving constantly through the sulphur clouds. That seemed to be their chief amusement."
I asked how hot the lava is in the molten lake, and learned that its heat varies according to the amount of gas given off, the more abundant the gas, the higher the temperature of the molten lava. This, it appears, was an important discovery made by the Americans.
"During months that we spent studying Kilauea," said Dr. Day, "we took almost daily observations of the temperature of the molten lake, and found that this varied considerably from day to day. At some periods it was as low as 1060 centigrade, and at others as high as I 175 degrees."
These temperature observations were taken with a pyrometer, a kind of telescope which allows one to get the temperature of a luminous burning object, even a distant one, by merely looking at it. Beyond the eyepiece of this instrument, and directly in the line of sight, there is placed a tiny electric light, which is seen against the object to be studied. By varying an electric current, this electric light within the telescope can be given any desired shade of color from dull red to the palest yellow, each one of these shades corresponding to a known temperature previously determined in the laboratory. Consequently, when the brightness of the little light exactly matches that of the distant burning object, it can be said that the latter has the temperature indicated on a prepared scale. In this way the temperature of stars billions of miles away may be known with great precision.
The scientists worked busily during the important hours that they spent in the crater. There was the pipe-line to be laid, the joints to be tested, the pump to be made ready, and finally the elbow of iron pipe to be thrust into the glowing lava dome. There were also observations to be made, specimens of lava to be gathered, and photographs of the fire-pit to be taken. It was an exciting time, but again all went well, and at eleven o'clock they were back on the rim with their hopes fulfilled. Carefully sealed in glass tubes were specimens of uncontaminated gases such as no scientist had ever drawn from a volcano.
"Was n't the iron pipe that you thrust into the lava dome affected by the heat and by the gases?" I asked.
"Yes, it was almost eaten away; that is, the short elbow about a foot long that penetrated the dome was eaten away. The six-foot length outside the dome was lined with glass, and was therefore not affected."
"Did not the iron of this elbow that was eaten away affect the gases collected?"
"No, because the lava of Kilauea contains about ten per cent. of iron oxid. So we introduced no new element into our gas specimens; we only increased slightly the percentage of iron, and in our analysis we made allowance for that."
"How about water in these virgin gases? Did you find any? Was your investigation conclusive?"
"Absolutely. The analysis of our gas specimens obtained in fifteen minutes pumping showed not less than a pint of water. And there is every reason to believe that this proportion of water is in the volcano as an original element, like the sulphur or the silica. It did not come from the air or the rains or the ocean. It belonged there."
To explain the significance of this discovery regarding the water would take us too far into the chemistry of rocks, a fascinating, but difficult, subject. The point is that by their descent into Kilauea these American scientists settled once and for all a disputed point that has an important bearing upon volcanic phenomena: the water was there in the volcano from the beginning.
On the day following this successful effort, preparations were begun for a third descent, with vacuum collecting-tubes of a different form, which might have given even better results; but before these tubes were ready, the lava dome had collapsed, and the spot visited by the Americans was covered by the molten lake. Nor did another suitable lava dome make its appearance for many months.
A few weeks later, however, one of the scientists again descended into the crater, and this time he had a trying experience. As he was clambering over the long slant of lava debris that spreads out from the foot of the precipice toward the molten lake, he suddenly realized that the dreaded shift in the trade-wind had come; the rotary movement about the sides of the bowl was beginning, and for five minutes he was caught in a vortex of strangling, swirling volcano gases. In this peril he found a little relief by crouching as near as he could to the crater floor, where ran a thin layer of cooler and purer air. Then fortunately the wind shifted back again, and the danger was past.
In this last descent remarkable photographs of the crater at a period of extreme activity were secured. Never were pictures taken in stranger surroundings. At the edge of the molten lake, only a few yards back, the explorer set up his camera. The tripod rested on hot lava rocks. The lens looked into a seething caldron, where great yellow bubbles rose and burst in luminous showers. Black boulders splashed into the fire flood, turned over slowly, and sank. In one place a shining molten torrent, red and yellow, poured under a natural bridge of lava rock, while out in the lake thick fountains of fire gushed up like geysers. It was a formidable display of fireworks, with frequent explosions, and the photographer caught what he could of it. His most remarkable picture was taken when the playful volcano hurled up a forty-foot fire fountain, so near that its heat scorched the camera-box. The explorer sprang back in alarm, and his clutching at the bulb was purely automatic; but he got the photograph.
One of the most startling phenomena witnessed by the explorers during their study of Kilauea was a cascade of lava that burst out suddenly from the precipitous wall of the crater forty feet above the molten lake, and poured down steadily for three days and three nights. It poured in several diverging streams, forming a fiery, fan-shaped cataract about forty feet wide at its base. Each one of these spurting lava streams was at least two feet thick, so that, in the whole mass, hundreds of tons of liquid rock must have flowed away every hour.
The sight of this awe-inspiring flood led the observers to one important and obvious conclusion; namely, that the subterranean reservoir from which the molten lake drew its lava supply could not be the same reservoir that fed lava to this cataract in the wall of the crater. Had such been the case, the law of pressures in communicating columns would have required the same level for the summit of the lava cataract and the summit of the lava lake, whereas one was forty feet above the other. Whence, then, came the lava in the cataract?
This brings us to the great question that has never yet been really answered—What is the fundamental cause of all volcanic activity? Nobody knows, but Dr. Day suggests a theory that may explain how the activity of a volcano like Kilauea proceeds and persists for long periods, once it has started. Let us assume that the inside of our earth is a fiery mass with about the average density and rigidity of steel; also that volcanic phenomena occur only at the extreme surface of this mass, in an outer layer that cannot, according to scientists, be more than sixty or seventy miles deep, which is like the varnish on a six-foot globe. Now, in this outer layer we have a long, narrow tubular opening that reaches down into the earth for five or six miles, and perhaps more. This opening is filled with molten lava that remains molten for months or years or centuries. What keeps it molten? Evidently heat from below; but why is this heat confined to a long and narrow tube? Why is not the whole mountain melted, if there are wide-spread fires below? And if there are not wide-spread fires below, why does not the long, narrow tube cool off and become plugged with hardened lava and end its activity?
Dr. Day's theory is that the depths of a volcano like Kilauea are not hotter than the surface opening. On the contrary, he believes that they are much cooler than the surface, his idea being that one great source of volcanic heat, perhaps the chief source in most present-day volcanoes, is the reaction between gases set at liberty in the operation of the volcano. And as far more of these gases are set at liberty in the upper regions of the volcano than in the lower, he concludes that the upper regions receive far greater quantities of heat.
But why, we ask, are more gases set at liberty in the upper regions of a volcano than in the lower regions? It is a matter of pressure. These volcano gases are held in solution in the molten lava exactly as carbonic-acid gas is held in a siphon of water. They are quite inactive as long as the valve is closed, but let the valve be opened, let the balance of terrestrial forces be disturbed, and straightway with a lessening of pressure comes a bursting and bubbling forth of gases from earth or bottle. The principle is the same.
In the case of gases deep down in the earth, it is certain that as soon as they are set free by any cause they rush together in violent reactions with a great production of heat. This extra heat causes a rising current in the lava column, which, as it ascends, is subjected to less and less pressure from above, and consequently liberates more and more of the gases that it has held in solution. And these gases, continuing to react violently among themselves, produce more and more heat as the rising current nears the surface of the crater, and a maximum heat production comes as the great gas bubbles burst into the air.
Then what happens? The lava is now empty of its gases; it is dead lava, chilled by the air and heavy. So it sinks by its own weight, forming a downward current in the molten column that may take it back again to the very depths of the volcano, where it will once more be charged with virgin gases. Then it may again rise to the surface of the crater, and thus continue rising and descending in one or the other of two lava currents that move up and down the long tube like buckets in a well, charging themselves with gases from the boundless store below and belching these gases forth in various combinations, with immense production of heat at the mouth of the volcano. Dr. Day found that in some cases these lava currents surge through Kilauea's molten lake at the rate of five or six miles an hour.
This theory also helps us to understand the formation of huge wells or perpendicular tunnels in Hawaii, which descend straight down through the lava rock for hundreds or thousands of feet, keeping a fairly uniform width of twenty feet more or less. How did these strange shafts come into being? Who dug these immense holes? Who bored them out so round and straight and true? Who glazed and fired portions of these perpendicular walls, making them look as if they had been treated in a porcelain furnace? No man, evidently. No man would have had a motive to do this work, even supposing human strength equal to the task of removing thousands of tons of rock to an unbelievable depth. These great wells were unquestionably eaten out by volcanic fires. But how? Not in any explosive way, for then the walls of these tunnels would have been shattered and their present symmetry destroyed. We must believe that, through some change in conditions below, there came a rupture and release of pressure at a certain depth in the lava rock. Gases were set free, and rushed into new combinations, with considerable production of heat. This heat melted the lava in that small area, and, not stopping here, melted more lava in the layer above, and so on until, layer by layer, a shaft two hundred and fifty feet long and twenty feet across was melted upward just as a candle-flame might burn its way upward through a disk of wax, until the pressure was entirely relieved by perforating the surface or the gas became exhausted.
"Has any one ever gone down into one of these shafts?" I asked.
"No," was the reply, "although Professor Jaggar, who is in charge of the Hawaiian Volcano Research Association, once planned such a descent. All his preparations were made, including a rope ladder several hundred feet long that he meant to use; but at the last moment it was decided that the thing was too dangerous, and nothing was done."
"Why is it dangerous? Is there hot lava down in these shafts?"
"No, but the rock is friable and treacherous at the mouth; besides that, it overhangs the shaft so as to give a very insecure footing."
Dr. Day described one of these great shafts near the crater of Mt. Hualalai, a volcano that stands at the west of Hawaii and rises to a height of 8200 feet. This shaft is about twenty feet in diameter, and is believed to be two or three thousand feet deep. If a large stone is dropped into its mouth, there is no sound of striking heard until many seconds have elapsed.
"Would n't it be possible to set up a windlass on timbers over the mouth and lower a man down with piano wire?" I asked.
"I suppose it could be done, but it would be difficult. The shaft opening is eight thousand feet above sea-level. It would be difficult to drag windlass and timber eight thousand feet up the sides of Hualalai. It's rough going and steep."
"Would the results of such a descent be of scientific value?" I asked.
"They might be. We might get important indications, for instance, as to the causes that led to the original release of pressure at the bottom of the shaft. And such an explorer could tell us whether these shafts have passages leading out of them. It would seem as though there must be an outlet at the bottom through which the molten lava flowed away."