When the Professor visited the volcano, he says the surface of the disrupted mass lay 740 Dan. feet lower than its original level; and according to Lieut.
Caroc's map a lake existed in the south-eastern part of this, nearly circular in form, and 4,400 Dan. feet in diameter, its water lying at an altitude of 2,885
Dan. feet above sea level. Watts makes no mention of any lake, therefore in all likelihood none existed at the time of his visit, the one seen by Caroc being formed by the hot water streaming from the gorge, and the surface water in Askja draining into the abyss during the twelve months that had elapsed since Mr. Watts was there. In 1878 I found that in the two years' interval since the Professor's visit the lake had greatly increased in size, its water then covering the whole surface of the subsidence to a considerable depth ; and from the level of the water p this year (1880) I should say that it had risen quite forty feet since 1878. This is only what was to be expected, as in all probability the greater part of the snow and rain which fall over an area of nearly twenty square miles drain through radiating rifts into the abyss. The Professor states that he found the temperature of the water 22° Celsius = 104° Pah., but when I tested it in 1878 it was only 97° Fah. Having, unfortunately, in the hurry of landing my luggage at Akureyri forgot both my Aneroid and my thermometer, I was unable to ascertain the temperature of the water this year, nor with exactitude how much it had risen since I was here last.
The quantity of water must continue to increase, there being no outlet, and in the course of some twenty years, should no eruption take place in the meantime, and open fissures to admit the water now collected into the heated depths below, the basin formed by the subsidence will be completely filled. This large and ever increasing lake in the bosom of an active volcano is a most alarming feature; it is extremely likely that when the water rises high enough to invade the gorge that it will find its way below and cause an explosion that will let the whole contents of the lake come in contact with the molten matter that it is reasonable to believe will lie at no great depth, a terribly violent explosion must inevitably ensue, one that will be likely to cause an earthquake to which those of 1872 and 1875-which opened rifts, it will be remembered, thirty miles in length at a considerable distance from the volcano-will be comparatively insignificant, one that will in all probability not only split the mountain into sections to the level of the Odáńahraun, and thus make Watts' description tolerably correct, but also send back the tide of molten matter in the channel connected with the earth's molten interior underlying Europe, in a way that may cause considerable volcanic disturbance on the Continent, there being reason to believe, as before observed, that such a channel does exist, and is connected with Iceland, the great Lisbon earthquakes in 1755 being preceded by the commencement of terrible eruptions from the Kdtlugjá, which lasted a year, while the Calabrian earthquakes, thirty-two years later, were followed by the outbreak of the prodigious lava-floods in the vicinity of the Skaptár Jókull.
Being pretty well tired out I now rejoined H., and lay down on the slope of the ' Pumice Crater5 for a short time, to recruit and partake of a little food before setting out to recross the lava-covered amphitheatre. During our rest we watched with considerable interest the gyrations of a pillar of sand about 200 feet in height whirled up by the rotary motion of the winds in Askja. This pillar travelled all over the crater in a most remarkable manner-now coming menacingly towards us, as if it would overwhelm the daring invaders of a spot where earthquakes have their birthplace, and anon retreating towards the south-west gap, as though beckoning us to retreat at once in that direction before harm befell us. This phenomenon is easily accounted for. In the north and east of Iceland, during the summer months, sea breezes prevail, which gradually increase in strength from very early morn till four or five o'clock in the afternoon, after which they gradually subside. These sea breezes are due to the air above the OddSahraun, rarified by the heat of the sun refracted from the lava^ constantly ascending during the day-timex the cold air-currents from the sea rushing in to take its place. To-day these winds appeared to meet in Askj'a another air-current coming from the icy wastes of the Vatna Jokull in the south, and formed a whirlwind which whirled up the light pumiceous sand and fine ash in the manner described. While resting I made a couple of sketches of the crater, one looking towards the western gap, in which I included this pillar of sand, and from these, since I came home, I have made a couple of water-colour drawings, which convey a very fair idea of Ashja as seen at this time.
Somewhat refreshed with our rest we now set out to recross the crater. How we each longed for a pair of wings to bear us over the four miles of rugged lava that intervened between us and Einar and our steeds ! but, alas! longing availed nought! and though we were in a spot weird enough to be the home of Genii, none appeared with the wished for wings. Shortly after we had passed the pumice, deluded by a somewhat level tract of lava, we took a more westerly direction than we had taken on our way over to the site of the 1875 eruptions. This led us into a labyrinth of fissures, and finally brought us face to face with an extensive bed of exceedingly-rugged and comparatively new-looking lava, which had welled up through a rift but a century or so ago. This was the newest lava I saw in Askja, though I saw some newer - looking on the outer slope of the mountain east of the entrance to the pass; therefore, probably, it is the last which issued here. We debated for some little time whether we should skirt or cross it, finally deciding to do the latter. We found it terrible hard work, and were compelled to sit down and rest every few yards or so. When I started from the ' Pumice Crater' I had my pockets laden with about a quarter of a hundred-weight of fragments of various kinds of rocks; but every time that I sat down I examined these to see if there were any not worth the trouble of carrying farther; some of the pieces 1 handed to Arni to carry, who took them very reluctantly, the bulk, however, were by degrees thrown away, each succeeding rest seeing one or more of the specimens abandoned which at the rest preceding I had determined to preserve; greatly to the amusement of H., who is not disposed to subject himself to the least inconvenience for the cause of science. When we ultimately reached the spot where we had left Einar, Arni and I had not a fourth of the quantity with which I started. It took us five hours to reach him; and I shall never forget poor H., who was the last to arrive, he was completely beaten, and it took him at least half-an-hour to cross the last two hundred yards of lava.