By Aneroid (in 1878) the summit of this crater has an altitude of close upon 3,800 feet. Taking the depth of the pumice at its base at 100 feet, and the height of the outer crater walls at about the same, the superficial lava in Askja at this spot lies 3,600 feet above sea level. Thus the altitude by my Aneroid agrees very closely with that marked upon Lieut. Caroc's map, viz., 3,660 Dan. feet = 3,768 English.
The view from the summit of this crater-cone within a crater is as unquestionably unique as it is wildly weird ; and one can form some idea of the terrible nature of the explosion that caused the earthquake on the memorable 4th January, 1875, from the veritable chaos of hugh masses of rock then disrupted and upheaved. The very slopes of the crater-cone, on whose summit we stand, rise on the south-west, at angle of about 5CT to a height of 600 feet from the surface of a tepid lake, whose bed was formed, as before stated, by the disruption and subsidence bodily into the abyss beneath Askja, of an enormous mass of the lava deposits lying in strata above it, oval in shape and five miles in circumference. From our coign of vantage, Askjas mountainous periphery can be seen to greater perfection even than from Jons Pass : on the south, distant but a little over a mile, the highest portion of it rises precipitously from the water's edge to a height of close upon 2,000 feet, while on the west, from the slopes of the crater round the north side of the lake, a distance of over two miles, the cliffs where the vast mass broke away rise a sheer semi-circular wall, 400 feet in height from the water to the level of Askja. This wall shows the lava deposits that have filled Askja's huge crater to its present level, en profile j and the stratification is so perfectly marked by the layer of scorias that has formed the surface of each deposit that it looks like a gigantic piece of masonry, fresh from the hands of Titanic masons ; but this was more noticeable two years ago than now, large masses having since then broken away in places; and still more so in 1876, when seen by Professor Johnstrup, who says that the fresh appearance of the face of the rocky walls from which the detached mass broke away is proof that the subsidence of the north-westerly portion at least happened as recently as during the 1875 eruptions. There can hardly be any doubt that the whole was disrupted at that time, not the north part only, for, seen from the cone-shaped crater through a powerful field-glass, the encircling cliff on the south-west, at its junction with Askja's mountain wall, appears as new-looking as farther north.
East of the lake, and distant from it about 700 yards, Askja's encircling mountainous periphery is a vertical precipice, at least 800 feet in height, for nearly a mile ; and it is evident by the face of this and the nature of the slope therefrom to the lake, that the slope is a huge slice of the mountain that at some period during the eruption had been blown bodily inwards. The explosion which hurled aside this immense mass opened a rift at least 200 feet within the mountain, the course of the rift being clearly traceable, though filled with debris, by a line of fumaroles, around which I noticed a trifling efflorescence of sulphur. This was the only place on the site of the 1875 eruptions where I noticed any signs of this mineral. Branching off the southern end of the rift, but divided from it by an angular rocky ridge, a deep gorge runs in a south-easterly direction for some distance into the encircling mountain, and here the immense volumes of steam, seen from the further side of the crater, were roaring forth.
From the above the reader must try to form some idea of what the scene of the 1875 eruptions in Asly'a is like, for I must confess I am unable to give anything like an adequate description, and I doubt if even the pen of a Dante could do so, though, perhaps, the pencil of a Dore might.
My companion, H., whose respiratory organs are none of the best, now declined to go farther, therefore Ami and I continued our explorations alone. With considerable difficulty we made our way over the rocky debris, lying in the rift, to the gorge in the south-east. Climbing to the summit of the rocky ridge, bordering its mouth on the north, that we might command as good a view of it as possible, we could see, when the wind for a moment wafted the clouds of steam away, that the gorge extended in a south-easterly direction from the waters of the lake into the mountain for close upon a thousand yards, and that its declivities were too precipitous for a descent to be practicable without a long rope, with which, unfortunately, we were unprovided. I endeavoured, but fruitlessly, to borrow one at Svartdkot before setting out for the volcano; and I now greatly regretted that I had not brought one from England, there being reason to believe that very large Geysirs exist in this part of Askja. The bottom of the gorge lay about 600 feet below the spot where we stood, and 50 above the surface of the lake, from which it slopes gradually upwards. Huge volumes of steam-I feel almost certain, likewise hot-water-belched forth at intervals from about a dozen large holes, or rifts, with such violence that the rocky ridge upon which we stood trembled. There were also a large number of small jets of steam jetting out horizontally from holes in the precipice opposite. Owing to the vapoury clouds that accompanied the more noisy outbursts we were unable to see whether any water was ejected or not; however, I think it almost certain such was the case, and that one or more Geysirs here exist, the stream of steaming hot water that was flowing down to the lake being too considerable to have been formed by condensed steam alone. By the violence with which the steam here escapes it is evident that even at this time, five years after the eruption, the heat in the volcanic vent, of which Askja is the outlet, must be intense, and the pressure of steam very considerable, and that were it not for the vents, indeed, safety-valves would be the fitter term, which here exist, another terrible eruption might at any moment take place.