United States or Myanmar ? Vote for the TOP Country of the Week !
The outer cone of Vesuvius, or Monte di Somma, rises from a circular platform by a moderately gentle ascent, and along the north and east terminates in a craggy crest, with a precipitous cliff descending into the Atria del Cavallo, forming the wall of the ancient crater throughout half its circumference; this wall is formed of scoriæ, ashes, and lapilli, and is traversed by numerous dykes of lava.
As far as we could see, the substance of the hill seemed to be of basaltic lava, which was mostly covered with the lapilli which I have spoken of before as ashes and volcanic sand. Even before we reached the pine-forest there was evidence of the action of water, which had covered the slope of the mountain with beds of thick compact tufa, composed of these lapilli mixed with fragments of lava.
But although we have no reliably historical record of volcanic action amongst the mountains of the Mont Dôme group, the fact that these are, comparatively, extremely recent will be evident to an observer visiting this district, and this conclusion is based on three principal grounds: first, because of the well-preserved forms of the original craters, though generally composed of very loose material, such as ashes, lapilli, and slag; secondly, because of the freshness of the lava-streams over whose rugged surfaces even a scanty herbage has in some places scarcely found a footing; and thirdly, because the lava from the crater-cones has invaded channels previously occupied by the earlier lavas, or those which had been eroded since the overflow of the great basaltic sheets of Mont Dore.
Besides these are others formed of stratified tuff, with interior craters, surrounding in mural cliffs eruptive cones of scoriæ, ashes, and lapilli; these cones are scattered over the isthmus and shores of Waitemata and Manukau.
One of the De Saussure family, who was in Mexico a few years back, describes Jorullo as consisting of three terraces of basaltic lava, which have flowed one above another from a central orifice, the whole being surmounted by a cone of lapilli thrown up from the same opening, from which also later streams of lava have issued. The celebrated cascade of Regla is just behind the hacienda.
These products of an explosive volcano are sometimes called cinders and ashes, because of their resemblance to the slag and refuse of furnaces. In the case of the volcano which we are studying, the lapilli are so black that they give the cone the appearance of being darkened by the shadow of a cloud, and on this account the peak is named Shadow Mountain.
Molten lava accompanied them, and a new volcano came into life in the valley where Cinder Cone now raises its dark, symmetrical slopes. The eruptions were violent. With explosive force the molten lava was torn into fragments, and sand, lapilli, and bombs were hurled out into the air. The finer particles were carried by the air currents far over the surrounding country.
We observed, that when lava abounded, the projection of rocks and lapilli either ceased altogether, or became of small amount. The whole eruption ended in a shower of impalpable ashes, which hid the mountain for many days, and which were carried to a great distance by the wind. Sometimes the ashes were pure white, giving the mountain the appearance of being covered with snow.
Many fell back again into the crater, but a large portion were thrown in fiery showers down the sides of the cone. At length, these beautiful eruptions of lapilli ceased, and the lava flowed more abundantly, though, being intermittent and always issuing from the summit, it was quite harmless; volumes of smoke and vapour rose from the crater, and were carried by the wind to a great distance.
At last, one evening, in November, 1868, when one of my daughters and I were observing the mountain through a very good telescope, lent us by a friend, we distinctly saw a new crater burst out at the foot of the cone in the Atrio del Cavallo, and bursts of red-hot lapilli and red smoke pouring forth in volumes.
Word Of The Day