Through Magic Glasses and Other Lectures / A Sequel to The Fairyland of Science

by Arabella B. Buckley

It was about eight o'clock in the evening when we started in a carriage for Resina, and alighting there, with buried Herculaneum under our feet, mounted our horses and set forward with the guides. Then followed a long ascent of about two hours and a half through the dark night. Silently and carefully we travelled on over the broad masses of slaggy lava of former years, along which a narrow horse-path had been worn; and ever and anon we heard the distant booming in the crater at the summit, and caught sight of fresh gleams of light as we took some turning which brought the glowing peak into view.

Our object was to get as close as possible to the newly-opened crater in the mountain-side, and when we arrived on a small rugged plain not far from the spot, we alighted from our horses, which were growing frightened with the glare, and walked some distance on foot till we came to a ridge running down the slope, and upon this ridge the lava stream was flowing.

Above our heads hung a vast cloud of vapour which reflected the bright light from the red-hot stream, and threw a pink glow all around, so that, where the cloud was broken and we could see the dark sky, the stars looked white as silver in contrast. We could now trace clearly the outline of the summit towering above us, and even watch the showers of ashes and dust which burst forth from time to time, falling back into the crater, or on to the steep slopes of the cone.

If the night had not been calm, and such a breeze as there was blowing away from us, our position would scarcely have been safe; and indeed we were afterwards told we had been rash. But I would have faced even a greater risk to see so grand a spectacle, and when the guide helped me to scramble up on to the ledge, so that I stood with my feet within a few yards of the lava flow, my heart bounded with excitement. I could not stay more than a few seconds, for the gases and vapour choked me; but for that short time it felt like a dream to be standing close to a river of molten rock, which a few hours before had been lying deep in the bowels of the earth. Glancing upwards to where this river issued from the cone in the mountain-side, I saw it first white-hot, then gradually fading to a glowing red as it crept past my feet; and then looking down the slope I saw it turn black and gloomy as it cooled rapidly at the top, while through the cracks which opened here and there as it moved on, puffs of gas and vapour rose into the air, and the red lava beneath gleamed through the chinks.

We did not stay long, for the air was suffocating, but took our way back to the Hermitage, where another glorious sight awaited us. Some way above and behind the hill on which the Observatory stands there is, or was, a steep cliff, and over this the lava stream, now densely black, fell in its way to the valley below, and as it fell it broke into huge masses, which heeling over exposed the red-hot lava under the crust, thus forming a magnificent fiery cascade in which black and red were mingled in wild confusion.

This is how I saw a fresh red-hot lava stream. I had ascended the mountain some years before, when it was comparatively quiet, with only two small cones in its central crater sending out miniature flows of lava (see Fig. 38). But the crater was too hot for me to cross over to these cones, and I could only marvel at the mass of ashes of which the top of the mountain was composed, and plunge a stick into an old lava stream to see how hot it still remained below. Peaceful and quiet as the mountain seemed then, I could never have imagined such a glorious outburst as that of November 1868 unless I had seen it, and yet this was quite a small eruption compared to those of 1867 and 1872, which in their turn were nothing to some of the older eruptions in earlier centuries.

Fig. 38.

The top of Vesuvius in 1864. (After Nasmyth.)

Now it is the history of this lava stream which I saw, that we are going to consider to-day, and you will first want to know where it came from, and what caused it to break out on the mountain-side. The truth is, that though we know now a good deal about volcanoes themselves, we know very little about the mighty cauldrons deep down in the earth from which they come. Our deepest mines only reach to a depth of a little more than half a mile, and no borings even have been made beyond three-quarters of a mile, so that after this depth we are left very much to guesswork.