Art. XIX.—Crater of Ngauruhoe.
[Read before the Otago Institute, 10th November, 1908.]
The earliest accounts of the crater of Ngauruhoe, by Bidwill and Dyson, show that considerable changes have taken place since these pioneers made the ascent of the cone. The former, in 1839, describes it as “the most awful abyss that I ever looked into or imagined.” The stones thrown in did not strike the bottom in less than seven or eight seconds. It was impossible to get into the inside of the crater, as the sides seen were, if not quite precipitous, actually overhanging. Bidwill states that Ngauruhoe was in a state of activity at the time of his visit, and the steam prevented him from seeing more than 8 or 10 yards into the crater.
This description applies perfectly to the crater at the present day if the volcano be more than usually active and the crater is reached on the south or east side. From other statements made by Bidwill it appears probable that he ascended the mountain on the north or west, and on those sides at the present time the crater-floor is almost level with the wall. It is reasonable, therefore, to suppose that the crater is now very different in form from what it was when Bidwill saw it.
Dyson, in 1851, stood on the northern side of the crater. He says the lip was sharp, and inside there were large overhanging rocks of a pale-yellow colour. It was impossible to descend into the crater. This account corroborates Bidwill's statement, and emphasizes the fact that the crater had, in the middle of last century, steep walls all round—or, at any rate, on the northern side.
Professor Thomas, in 1888, called attention to the form of the crater, and recorded that Mr. Jackson Palmer, then engaged in work near the mountain, had noticed that after a long spell of bad weather in 1888 a gap had been formed in the east side of the crater-wall.
In 1887 Mr. Hill ascended the mountain, and at that time, and at a subsequent visit in 1892, the crater was in the same condition as it was in when I first saw it in 1891. Fig. 1, Plate V, gives an idea of its appearance. The small north-west-rim crater, called by Mr. Hill the “yellow crater,” was then rather active, and steaming vigorously. The main crater had a floor nearly level throughout. We entered the crater on the western side. Near this side there was a violent escape of steam, though less in amount than that which escapes from Karapiti. Smaller steam-jets were issuing in many places, and most of them escaped from the summit of a cone of bright-yellow sulphur 2 ft. or so in height. The effect of all these small cones was very pleasing. It was possible at that time to walk all over the floor of the main crater, though the ground was hot and in some places soft.
In 1893 the appearance of the crater had absolutely changed, though the small north-west crater still remained, but steamed much less than previously. All the small sulphur cones had disappeared, and near the centre of the main crater there was a deep black explosion-cavity. The explosion to which the formation of this was due had scattered mud and volcanic ash over the floor of the main crater, and had covered up the little sulphur cones. The explosion-cavity was then about 30 yards in diameter, and there was level ground between it and the north-west crater, and more between the cavity and western wall.
In 1891 a report was published by Mr. Cussen on the Tongariro Mountains, and with it an excellent map: but it is stated in the text that though Ngauruhoe was twice ascended, the clouds of steam that issued from it prevented the surveyors from obtaining a clear view of the crater. It is, however, stated that the crater was circular, and the small crater on the north-west side is described. In the map another small crater is indicated, on the south side. This is probably an error, for no mention is made of it in the text, and it was certainly not there in January of that year. Dr. Benedict von Friedlander was the first to call attention in writing to the “hole” in the south-west of the crater. He visited the mountain in 1896, and was unable to see to the bottom of the “hole” because of the large amount of steam that issued from it. He does not state the extent to which the “hole” encroached upon the crater on the north-west rim, to which he, like all other observers, refers.
In January, 1898, I was able to walk between the explosion-cavity, or “hole” of Dr. Von Friedlander, and the small north-west crater, though the explosion-cavity was then much enlarged, and the level ground between it and the north-west cone was much reduced. The cavity had also extended considerably to the west, though there was still some level ground between it and the north-west crater. As in 1893, I was unable to see to the bottom of the cavity, because of the large body of steam that issued from it, though a long time was spent on its edge. The activity did not seem so pronounced
as in 1893, for in that year from time to time a rumble was heard in the interior of the mountain, and dense clouds of steam and dust were shot up. It is probable, however, that there was not much difference in this respect, for after returning to camp a rumble was distinctly heard, and soon after the dark cloud rose up from the crater.
Another visit was paid in December, 1906, when the mountain was more than usually quiescent. It was found that the cavity had extended considerably towards the west, where now there was no flat ground between it and the exterior wall of the main crater. It had also extended towards the north-west crater, and had encroached on the small cone in which that crater was situated. During an interval when the steam lifted it was possible to see to the bottom of the cavity. It appeared to be nearly 200 ft. deep, with vertical walls on the east and north, but elsewhere bounded by steep walls, which on the west were a continuation of the wall of the main crater. The walls of the cavity were covered with jets of steam, and were encrusted with sulphur. At the bottom was a small lake of greenish-yellow water, on which masses of scum—probably sulphur—were floating, and there were specially strong steam-jets near the level of the water. At this time the crater certainly did not deserve the title of “bottomless pit,” given to it a little later by a Press reporter.
In February, 1907, the mountain became more active, and another visit was paid to it to find out whether the activity had caused any noticeable changes in the crater, and also to find out the exact nature of the violent explosions that occurred from time to time. A start was made early in the morning, when a dark cloud was rising 3,000 ft. above the crater. The appearance was then similar to that presented on the following morning, when the photograph was taken. When within 1,000 ft. of the summit it was found that the surface was covered with slimy mud to a depth of 1 in. The depth of mud increased as the summit was approached, when it attained a depth of 6 in. When 500 ft. from the summit the wind failed, and the black cloud rained mud on to the surface of the mountain. We were soon covered with mud from head to foot, but persevered in our ascent, though inky blackness enshrouded all the mountain-summit, and the air seemed filled with sulphur-dioxide. At the top it was impossible to see anything, nor were the sounds very different from those we heard on previous visits. Everything indicated that an explosive paroxysm had just ceased. The cold wind was so piercing that it was inadvisable to remain long at the top. We stayed as long as possible, but the air did not clear, and we had the satisfaction of seeing after our return that the black cloud still rested on the summit. The mud that fell on us had a strong acid character, for it bleached the colour from a print blouse that my wife was wearing. Previously, in 1906, Mr. Flower, of Christ's College, Christchurch, had agreed with me that the smell of sulphur-dioxide was much more pronounced than that of sulphuretted hydrogen, which goes to prove that the activity of the crater was at an unusually low ebb when Dr. Von Friedlander could detect the latter only during his visit in 1896. During this visit we were unable to see what changes had taken place in the crater, but it was evident from the foot of the cone that the exterior wall had suffered no changes. The gap in the eastern wall, to which attention was then called, was, as previously stated, formed in 1888. Although some overhanging crags at the side of the gap are in an extremely unstable state, and might be dislodged by the vibrations caused by a steam-explosion, no rocks have, so far as I know, fallen from it since the year 1891, when I saw it.
The photographs taken by Mr. Browne at Easter, 1907, and by Mr. Cockayne this year, do not show any material change as a result of the rather violent activity that was in progress when the photograph (Plate VI) was taken. It appears, however, that the extension of the deep cavity westward and northward has been continued to a slight extent. In all my visits to the crater the escape of steam from it has been much more voluminous than is shown in the photograph of the crater taken by Mr. Cockayne.*
There is one point about which I am not certain. A small mud-crater is to be seen on the east side of the big explosion-cavity. When it was formed I do not know; it certainly was not there in 1891. It may have been formed at the same time that the explosion-cavity was blown out, though I have no note of its presence in 1893.
To sum up:—
1. The form of the crater appears to have been very different in 1839 and 1852 from its present shape.
2. In 1891 the floor was level, except where the north-west crater was situated, which was then the most active spot.
3. In 1893 the north-west crater was less active, and the explosioncavity was of small diameter near the middle of the crater, and was steaming vigorously.
4. Since that time the explosion-cavity has extended westwards and northwards, and the activity of the north-west crater has dwindled.
5. No escape of lava has occurred within historic times.
6. The main-crater walls have not changed since 1891.
Explanation of Plates V-VII.
Upper part of cone of Ngauruhoe, at 8 a.m., 14th March, 1907. Photo taken from the south-east; distance, five miles.
Highest point of crater-wall of Ngauruhoe—the south-east side.
[Footnote] * “Tongariro National Park”: L. Cockayne. Parliamentary paper C.—11, 1908.