Popular Science Monthly/Volume 61/August 1902/Field Notes of a Geologist in Martinique and St. Vincent
|FIELD NOTES OF A GEOLOGIST IN MARTINIQUE AND ST. VINCENT.|
By Dr. THOMAS AUGUSTUS JAGGAR,
U. S. GEOLOGICAL SURVEY AND HARVARD UNIVERSITY.
THE extraordinary accuracy of the above prediction, printed ten years ago, has been forced upon the world's attention recently by the sad story that the newspapers have told of the volcanic disasters in the Caribbee Islands. The following notes and the accompanying illustrations were collected hastily in the field after a month spent in incomplete study of the two volcanoes and their effects. Such notes necessarily contain inaccuracies; they may be more accurate, however, than many of the fairy stories that have gained currency in the dailies, and if I succeed in correcting some false impressions that have gone abroad about the meaning of these eruptions from the scientist's standpoint, I shall accomplish all that is necessary prior to more complete and accurate publication as the product of laboratory research at home. When the first news of the explosions reached America the newspaper accounts proved marvelously accurate; when half a hundred correspondents reached the field the degree of accuracy waned—probably directly as the public interest, which needs fiction to keep it alive. It is to be hoped that when the magazine stage of recording the Caribbean eruptions is reached, the truth curve will rise once more and the facts assert themselves. Even here—I write from Barbados—the most remarkable statements are solemnly believed; victims were found with their intestines charred and the outer skin untouched; a man was found seated on the box seat of a carriage in a lifelike position, twirling his moustache; scientists assert that the whole island of Martinique is likely to blow up at any minute, and great rents traverse the island from end to end; St. Vincent is in flames, a hundred minor craters have broken out, not a living green plant persists on the island and vessels cannot land; can scientists say that those eruptions have no parallel in history, and the electrical and gaseous phenomena make them unique—these and a hundred other similar statements have absolutely no foundation in fact, while other most interesting details have passed unnoticed. The fault,
however, does not rest with the correspondent; it rests with those at home who 'cook up' cable despatches, and with those living in the islands whose nerves are gone and who are thereby in an overimaginative frame of mind. Thus while I was occupying a beautiful little villa under the leeward slopes of Soufrière, a small thunderstorm broke about
midnight over the mountain—thunderstorms occurred nearly every day. It was described next day as follows in the local paper:
With such an account ten miles from the scene of action, it is not remarkable that the story has lost all semblance of truth when it reaches New York.
When the scientists were embarking on the Dixie, they were constantly asked 'Well, doctor, just what do you expect to do when you get to Martinique?' It was at that time a difficult question to answer, but may now be answered by telling briefly what we have done. The
Dixie arrived at Fort de France at daylight, May 21. At 10:30 that morning a party of officers, scientists and correspondents were taken on the Potomac to St. Pierre and landed. The second great eruption of Pelée had taken place the day before, so that every one was on the alert, and we were warned by Lieutenant McCormick, commanding the Potomac, that if the tug's whistle blew we were to make for the boats at once. We wandered through the dreary ruin, which has been described. I was impressed by the completeness of the destruction of the masonry and the absence of visible large volcanic fragments. The streets were filled with masonry rubble, mostly rounded sea-worn bowlders, and everything was coated with green-gray powder or sand. The roofs were gone, an occasional timber was burning, bodies were still numerous if one went into the houses and looked for them. There was a baby in an iron cradle, a man face downward in a tank, and a man lying on his
hack in a deep baker's oven. One of the party found eight or ten bodies crowded together at the foot of the cliff. The end of the town toward the volcano is deeply buried under fallen sand or gravel—the southern end has a covering of only a foot or two. There is a great change in the aspect of the city now, since the later eruptions, from the condition shown by photographs immediately after the destructive blast of the eighth of May. It seems agreed by those who witnessed the eruptions that the explosion of the twentieth was greater than the first one. In any case, the second blast demolished third stories and leveled the second belfry of the cathedral—the heap of beautiful bells, the chimes 'whose soft, liquid notes used to ring across the water of the bay with touching cadence at the Angelus hour'—they lie tumbled in rubbish, splinters and steaming vapors, their ancient engraved inscriptions half buried in dust. The bodies found were mostly shriveled to a crisp—this too was in part the effect of the second hot blast of the twentieth, for many of the bodies found earlier were described as being not much altered, and some such are shown in the accompanying photographs. The odor was not especially bad, but it is a haunting 'smell that one dreams about afterward; it is a combination of foundry and steam and sulphur matches and burnt things, with every now and then a whiff of roast or decayed flesh that is horrible.
I had returned over the heaps of rubble along the Rue Victor Hugo, the main street parallel to the water front, to a point not far from the landing, and looked about me. It was impossible to realize that this ruin had been a thriving French city just one fortnight previous; literally not a roof was left the whole length of the city for two miles, and scarcely a timber; nothing but twisted iron and masonry and corpses. Here and there steam rose through little holes in the wet brown sand over a pile of cobbles, and a sickening whiff of it showed whence it came. I found a dead cow in a back stable-yard, and a lot of children's toys, and the dishes set on a dinner table; but one must needs search for these things. Almost everything is buried under fallen walls. The tropical architecture, almost wholly cobblestone masonry and pink plaster, with open courts, alleyways and inner gardens, strongly suggests Pompeii; a wooden New England town could not have persisted three hours in the presence of the giant blowpipe that destroyed St. Pierre; it would have been simply burned up and blown away as ashes. The timbers of St. Pierre are practically gone. I looked toward the gray old volcano, whose summit was shrouded, but the lower slopes were sunlit and silent and powdery; the whole landscape is powdery, like old statuary with a dust coating that makes stronger the modeling of the city; mountain slope and cliff are bare, the verdure of the Carbet hillside ends abruptly along a sharp line, and there begins the new volcanic landscape, clean chiselled, rocky, weird, gray, uniform, without any color, without any motion except steam-jets on Pelée's slopes. But look! What are those steam-jets doing? There were one or two along the sea-front when we landed, but now there are eight, ten, twenty, and they are spurting higher all over the slope. Dr. Church was standing near me and saw me watching them. We did not either of us like the look of it. Now there were about forty, like so many ghostly locomotives that had run out from their tunnels in the volcano roundhouse and were all getting up steam at once. White-coated officers and men of science were to be seen in groups here
and there far away among the ruins and on the higher walls and slopes, but they were under the cliffs out of sight of Mont Pelée. We looked towards the Potomac; yes, she had seen it too, and a white steam-jet from her preceded the sharp blast of her fog-horn as she sent out a quick-repeated summons for all to return at once. Pell-mell they came tumbling to the water front and there was always someone else who had not turned up yet; the white-coated jackies were in place and the boats started from the shore. No sooner were they clear of the
Fig. 8. St. Pierre: Interior of a Home. Woman, girl and boy. The living figure is Dr. Haven, U. S. Consul at St. Kitts. Photograph taken May 19, the day before the second great eruption.
|Fig. 9. St. Pierre: A Victim.||Fig. 10. St. Vincent: One of the Injured.|
landing than two more figures appeared and we had to put back for them. Meantime the mountain was sending up clouds of steam from all over its slopes as though it were rifting in a hundred places preparatory to a titanic outburst. But it did not do anything, and I now strongly suspect that what we saw was the product of a smart shower over the mountain from the clouds lowering on its summit. The cool water rills running down the slopes come into contact with beds of hot dry gravel previously thrown out. Wherever such a contact is made a jet of steam at once is formed; we had opportunity to see much of this action later on at St. Vincent, and it is this process that has given rise to many stories of small craters forming.
We spent another day among the ruins, exploring St. Pierre to the mountain slope at its northern end and to the steep roadways that climb the southern cliff. The city was in a cul de sac, hemmed in by a cliff south, a higher cliff east and the ocean west; its northern end was on the actual foot slope of the volcano. The present crater was blown clear of clouds as we steamed past and we saw a cup-on the summit open to the west, walled in on the east, with a huge pile of scaly looking hot bowlders in its midst steaming violently. At the distance from which we saw it, it was estimated roughly that the cup would measure perhaps 2,000 feet across by 800 feet deep. This crater ends in a deep gulch west that extends down to the sea; old photographs show that this gulch was there before the present eruptions. Apparently it was down this gulch that the mud flood came winch overwhelmed the Guerin factory. All along the foot of the mountain are steaming fan-shaped deltas of débris, and far up the slopes these are matched by leaf-shaped arroyos or deep trenches hollowed out of the old earthy volcanic beds of which much of the island is composed. This trenching has been accomplished by the cloud-burst torrents of water laden with grinding sand that fell during and after the eruptions—in part condensed steam and in part heavy rains that recently have been exceptionally abundant. Much of the material which fell in the first outbursts of probably both Pelée and Soufrière was dry and red hot; it was relatively fine, the largest fragments falling near the vent. The grades of the hillsides were already steep and it is probable that this material flowed somewhat like dry sand. This, if seen at night, would account for the reports current of glowing molten lava on Pelée. When I was in Martinique there was no sign of molten rock, nor have I seen any in St. Vincent, and the greater part of the evidence at present makes these eruptions purely steam explosions which have blasted out and comminuted large quantities of the old country rock, or bedrock of the islands, itself an ancient volcanic product.
Fig. 11. St Vincent: The Soufrière Volcano and the Steaming Gravel Beds of Walliabou River Looking N. E. The steep sea-cliffs shown are the product of submarine landslips. Under the 45 feet of sand, gravel and boulders heaped in the foreground, Richmond Village is buried. This corner is the St. Pierre of St. Vincent in location and effect of the explosion. Note the coating of wet sand above the fiery gravels up the Walliabou and at its mouth. Photograph taken by C. Taylor of St. Thomas, May 31, 1902, the day of the ascent of the leeward slope; the climbing party were on the crater's edge when this picture was taken.
On the 23d of May the Dixie landed us and a goodly store of supplies for the sufferers, at Kingstown, St. Vincent. There I left her, in company with Dr. Hovey and Mr. Curtis. It was with deep regret that we parted from Captain Berry, whose splendid hospitality had made the entire voyage a pleasure that all the guests on the ship will never forget. It was really the first parting from American territory, for on a man-of-war one feels rather safer than on land. Good friends sprang up, however, among the hospitable English colonists, and supplies, houses, servants and horses were furnished us before we could ask for them. The government supply steamer Wear was on several occasions placed at our disposal, so that we coasted around three fourths of the shores of St. Vincent before going into the interior at all. We saw the Soufrière in partial eruption in clouds and rain; we landed at Georgetown on the fatal windward coast and visited the hospitals, where opportunity was given for interviews with the scorched victims of the explosive blast of hot cinders that had burned faces and ears and hands and feet, but curiously failed to burn clothing or houses. The hot sands, when they fell on these people, seem to have been at a temperature hot enough to inflict scalding wounds, but not hot enough to ignite anything or burn through coverings. On May 29 we proceeded in a long dug-out canoe rowed by five stalwart blacks to Chateau Belair, and from that point explored the west coast of the volcano proper and made a successful ascent to the edge of the great crater on a brilliantly clear day. The following week we made a similar ascent from the eastern or windward side, but reached the crater's rim in a most unpleasant black fog after a Tather perilous climb along precipitous wastes. After two weeks of most instructive work at St. Vincent, I came to Barbados, ninety miles to windward, to learn something of the dust which fell here in showers on the evening of the Soufrière eruption. This completes the itinerary of the writer to this date.The devastation at St. Vincent does not appear especially different from that at Martinique. The human conditions were different and the destruction of property wrought by the first eruption was much more widespread. In this respect, and from the size of the crater and greater diffusion of the dust, it seems certain that the Soufrière eruption was phenomenally much more violent than the eruption of Mont Pelée. The crater is more than twice as large as that crater of Pelée which I saw on May 21; the dust-fall has been reported from Trinidad, from Barbados, and from vessels at sea to the east and southeast at distances from one hundred to nine hundred miles from St. Vincent. At Walliabou sugar works southwest of the volcano, and in Richmond next to it, exactly the same fiery blast swept the cliff face as at St.
Fig. 12. St. Vincent: Avenue in Chateau Belair, showing the Soufriére in the distance Just outside of the destruction belt, on the west side of the island.
Fig 13. St. Vincent: Avenue from Richmond House to the Sugarworks, one mile from Chateau Belair. Just within the destruction belt showing the ruin of Richmond House. In location Richmond was the St. Pierre of St. Vincent.
Pierre. In the same fashion Richmond is buried, 45 feet deep at its northern end, 3 feet at the southern. In the same way the one masonry building in Richmond village was. thrown down, and five-foot blocks of masonry blown forty feet away from the mountain. The very odor over the ruin is the same. Just south of the Soufrière there is a group of high mountains. These blocked the passage to leeward southwest, and the heavier material thrown out of the crater's throat accumulated in the basin between these mountains and the volcano. Great drifts of fiery hot sand and gravel fell here and remained hot for weeks. The local torrential streams at the beginning of the rainy season, working on these beds, are converted into steam and make spectacular explosions, which alarm the natives, but are really quite harmless. At the sea-front west of the Soufrière there have been submarine landslips on a considerable scale, leaving in some instances vertical earthen walls 50 feet high where before there was a peaceful little village of thatched huts. The sea laps the foot of these unbalanced precipices, and a twelve-foot oar three feet from the strand-line finds no bottom. To a geologist one of the most remarkable effects of such an eruption is the rapid wearing away of the land that succeeds it. The protecting matter of tropical jungle has been burned and buried under two to ten feet of angular sand-grains; heavy rains cut torrent trenches in this material and all the old slopes are suddenly steepened by the falling away of the seashore and the piling of volcanic débris on all the crests of the land. The mountain is soaked in steam and water, local showers are at work all the time, and the result is like playing the hose on a steep mud pie; trenched and rill-marked in every direction, landslides are the rule in such topography and no slopes are safe. I landed for only a few moments to collect a specimen in one of the deep canyons northwest of Soufrière; a few blows of the hammer started a twenty-foot block of solid rock out of the gulch-slope a hundred yards away, and immediately afterwards a great bank of earth some twenty-five feet high came crashing down only a few feet from me. Needless to say I beat a hasty retreat to the boat from such an unstable land. We learned from this experience that the only safe place on new volcanoes is on the crest—unless one includes the Irishman's position, on 'leave of absence.'
There are a number of questions constantly asked of a geologist in this field, and some of these I must try to answer briefly here, without going further into a description of geological details. Was there any forewarning of the eruptions? Clearly there was; the prediction quoted at the head of this article was based on well-authenticated data. At Pelée, the lake in the crater was warm, and the smell of sulphuretted hydrogen perceived as far back as January. In April
Figs. 14, 15. St Vincent: The U.S.S. Dixie at Kingston unloading supplies for refugees; one of the Dixie's lighters unloading on the beach at Kingstown; a camp of refugees, using the U.S. tents sent by the Dixie, and a hungry family waiting for 'government rations.'
there were noisy rumblings and steam was emitted; actual eruption is reported from April the twenty-sixth on, and yet the city was not evacuated. In St. Vincent local earthquakes have been on the increase for a year in the neighborhood of the volcano; people were actually frightened away from Windsor Forest on the northwest slope of Soufrière, as far back as May, 1901, by rumblings and quakings. The water of the lake has been seen to bubble and sulphurous coatings are described as being deposited on the rocks. So violent were the signals early in May, especially when the news of the Guerin disaster came from Martinique, that the leeward slopes of the Soufrière, at all times sparsely inhabited, were abandoned. Hence the small loss of life on that slope. On both islands, if the respective governments had maintained vulcanological stations with instruments, doubtless, there would have been perceived a gradually increasing series of signals of different sorts, tremors, sounds, sights, smells and temperatures. This record, if we had it now, would be invaluable. It cannot be reconstructed.
The question 'What actually happened in the eruptions?' involves no very great difficulty. The eruptions were small manifestations of a common type. Probably the Plinian eruption of Vesuvius was similar; the Central American volcanoes have quite the same history;. Krakatoa in 1883, Tarawera (New Zealand) in 1886, and Bandai San in Japan in 1888, all present phenomena identical in the main, with local variations. A slip of some sort liberated a steam column; the cause of the fracture or the source of the steam is one step too far back into theory to venture to treat it here. Release once started followed old vents, water-holes, and these vents were Soufrière and Pelée. The explosion that followed release of pressure tore away the walls of the fissure and its violence ground the material to powder. The material came from a depth where the rocks were hot, and it was heated further by friction. Those who saw the eruption of Pelée on the twentieth of May describe a black column of dust and rocks that looked like smoke with wonderful purling, interbillowing nodes that overrode each other like cauliflowers or 'brains'; this column shot up silently at first, followed by heavy detonations that finally became a continuous roar. The column was estimated by Lieutenant McCormick of the Potomac to be at least five miles high; he witnessed the spectacle from Fort de France. Lightning shot through the great billows in all directions in a network. When it reached its maximum height the column spread out like a flower on its stalk and the upper edges of the hard smoke-steam masses were lighted white by the rising sun. A perceptible cold wave was felt. A shower of gravel took place followed by fine dust which continued falling for an hour. This was the day of the funeral of Consul Prentis. A visit to St. Pierre later the same day showed that a terrific blast had razed much that before had been upright, 'hot ashes were steaming at the water's edge, and there were immense bowlders lying in a bed of ashes.' These horizontal blasts are not hard to account for and do not
require a horizontal nozzle to project them. They are simply the result of the downblast after the heavy gravel has begun to fall, acting against the upblast from the throat of the volcano, and both together deflected and thrown into terrific whirls or tornadoes by the prevailing wind, which on Mont Pelée is northeast. St. Pierre is southwest of the mountain and the crater is somewhat overturned to the westward.
The death-dealing billows of falling hot sand and gravel, themselves a mighty downward wind, deflecting with them the rising hot steam and gases, finally rush down the mountain slopes in whatever directions they are guided by vale and ridge and wind. They were guided into the cliff-hollow of St. Pierre at Martinique and Walliabou at St. Vincent, both to leeward of the craters. In St. Vincent there was also an outrush symmetrical to the great crater in all directions, windward as well as leeward; hence the destruction of the windward estates. That there was tornado action is proved by the frightful demolition of masonry and the bending of trees; in St. Pierre this is away from the mountain and curving from south-southwest to southwest as we go southward from the volcano, these directions being shown by the downbent trees.
A common question is 'How were the people killed? Was it some strange gas? Were many killed by lightning?' There is no need for calling in any unusual gas; no doubt there were several gases present and the combustion of tropical vegetation made others that were highly explosive if mixed with air. This may account for some flame explosions reported as coming in from the sea-front at St. Vincent. The people of St. Pierre were killed by steam, hot dust, falling stones, falling buildings, drowning, burial alive and burning. The heat of a burning city fanned into a 'whirlwind of fire,' killed all who were left over from the other sources of death. The little city was as an anthill to a forest fire, in the presence of the terrible earth forces at work.
In conclusion let me say a word about the place of these eruptions in the geological history of the islands. They are not at all different from what the old cliffs, carved by the sea along the shores, show to have been the source of the heaping up of all the rocks that make the foundation stones the hills of these islands are carved upon. For these old sections are what geologists call agglomerates—masses of volcanic fragments, large and small, bedded in gravel and mud. Just such agglomerates are made anew by the great banks of dirt the volcano has vomited into the Walliabou at St. Vincent or Pelée into the gulch of the Factory Guerin. There are also old lavas interbedded with the agglomerates, showing that frequently the eruptions have been concluded in the past by the flowing out of molten incandescent rock. Perhaps this may come now, in the near future; even as I write there are cable despatches describing glowing lavas at Mont Pelee. The bared slopes of the Soufriere, devoid of vegetation, reveal a topography and geological structure so exactly like many things in our own Rocky Mountains that it is difficult to believe that one is in the tropics. There, too, in the tuff beds of the Yellowstone Park, is a fossilized tropical verdure which gives evidence that when those volcanoes of Wyoming were active, their slopes were covered by the vegetation of a warm climate near the level of the sea.