Description of the Great Fissure.

Map No. 2, attached to this report, is based on the recent topographical survey, made specially to illustrate the changes in the country which have taken place since the eruption. It will be seen that the result of such eruption is the formation of a fissure in the earth's crust running nearly straight on a true bearing of 58° for a distance of eight miles and three-quarters, extending from the north end of Wahanga to near Okaro Lake. South-west of this it is continued by earthquake-cracks for some miles further. The fissure varies considerably in width and depth, being widest at Rotomahana, where it has a maximum breadth of a mile and a half, whilst its general or mean width where it crosses the mountain may be stated as an eighth of a mile. The depth is greatest near the northern end, just between Wahanga and Ruawahia, where it is about 900ft. below "the gap," or 1,400ft. below the top of Ruawahia; and the least is at the southern end, where it may be said approximately to have a depth of 300ft. It must not, however, be supposed that the fissure has the appearance of a continuous rent or split in the earth's surface for its whole length; on the contrary, it is bridged in several places by parts of the original surface remaining in position. It presents, indeed, more the character of a series of craters (not necessarily circular), arranged in a nearly straight line and at various elevations above sea-level.

As it will be necessary to use the word "crater" very frequently, it is as well to explain that it is intended to convey the idea of orifices of very different characters, but all of which have been actively engaged in the ejection of solid matter, either in the form of molten rock and scoria; or sand, earth, mud, and unfused rock, accompanied in the latter case usually by water. The first description of crater is confined to that part of the fissure extending from the north end of Wahanga to the base of Tarawera; the second description extends from the north end of Rotomakariri to the Southern Crater; whilst the Black Crater combines the characteristics of both.

Standing on the highest point of Ruawahia, 3,770ft. above sea-level, and looking north-east, the fissure is seen to have passed along the steep wall-like face of Wahanga, cutting part of it off, and terminating near the northern end of that hill in a deep oblong crater, the eastern side of which is very much lower than the western. Immediately to the north of Ruawahia is a long deep crater, with nearly perpendicular sides, which cuts off "the gap" completely, and the western side of which is also much higher than the eastern, reaching tip, in fact, to the level of the Wahanga Plateau, whilst the opposite side is but little elevated above the lower plateau extending to Kanakana. The bottom of this fearful-looking chasm is about 1,100ft. below the top of Ruawahia. Its sides are so steep that a descent into it would be impossible. It is scorched and blackened by the heated matter from below, though here and there the rugged faces of the original lighter-coloured rock can be seen. The solid contents of it appear to have been blown clean out, and are scattered all over the country in fragments of various sizes, the larger and first-ejected portions being doubtless hidden by the black and reddish scoria which is now piled up on its edges. Some of this has fallen back again into the vent, and thus prevents a clear view of the more solid lava which is probably present at its bottom. It is separated from the most northern crater by a sharp ridge composed of loose scoria, which has fallen back from the air after being ejected, and which, no doubt, marks a point in the fissure where the molten matter met with some obstruction, or where activity first ceased. The lower walls of this crater are quite perpendicular, whilst the upper parts slope at a high angle to the surface. When the Survey party was there on the 28th July it was extinct, excepting that on the western side, near the Wahanga Plateau, steam escaped from a number of cracks, as it also did just outside the crater-edge on the eastern side. It is difficult to estimate the depth of newly-deposited scoria along the edges of these two craters; but it appears to be about 40ft. or 50ft., decreasing in depth as the crater is left.

The present height of the top of Ruawahia is 3,770ft. above the sea. The old station of the trigonometrical survey was 3,606ft. Its position was right in the centre of the fissure, and just to the east of the point lately determined, at a distance of about 250 yards. It follows from this that the depth of newly-deposited scoria is nearly 170ft. in that locality. From the position of the old station a line drawn on a true bearing of 62 for rather more than a mile will follow along the centre of the fissure in the direction of Tarawera. Along this portion, the width of which averages 250 yards, there page break

Plate No 4

The Great Fissure on Tarawera and Ruawahia Mountains.

Looking North-east.

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Tarawera. June 14th. 1886.

From sketch by S. Percy Smith.

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General View of Locality from Okaro to Tarawera taken from Ridge on Edge of Ashfield

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[unclear: Panorama] from the top Ruawahia

[unclear: Looking West]

page 47 are four distinct craters, whose depths vary from about 350ft. in the northern one to about 250ft. in the southern one, the central ones being the deeper—about 500ft. They are separated from one another by walls of loose scoria, which do not rise to the height of the east and west sides. As the violence of the first outbreak decreased, it would appear that the activity became more localized, and hence places were left where the escaping steam was insufficient to eject the scoria which fell on all sides from the more active parts of the vent, and thus allowed it to accumulate and build up the walls separating the several craters. Plate No. 4, which is taken from one of Mr. Spencer's photographs, shows the fissure as seen from the south-west end, looking north-cast. The separate craters will there be seen, with the steam rising from the sides in several places. The day on which the picture was taken was beautifully fine and the atmosphere very dry; hence but little steam is visible, though in the early part of the day it completely obscured the view.

The margins of the fissure have several little peaks of scoria, rising as much as from 50ft. to 100ft. above the general level, and the outer slopes of these descend at a considerable inclination to the lower parts of the plateau. (See Plate No. 4A.) Their structure is very evident to the eye, and illustrates exactly the ordinary formation of volcanic cones by the building-up of outwardly-inclined strata of loose scoria mixed with larger fragments of the unfused native rock. Inside the fissure the ejected scoria has fallen back so as to leave a steep talus sloping down to the bottom of the craters, though in many places the original rock can be seen protruding through it, sometimes partly fused and become scoriaceous, at others apparently unaffected by the passage of the heated matter.

Plate No. 5, looking along the fissure southerly, and across the deepest crater, shows very distinctly the surface of the older rocks, distinguished by their lighter colour; and here the deposit of new matter varies from 70ft. to 120ft. in depth. It will be seen also that this, the deepest crater, has much more perpendicular walls than the others. The margins of the fissures are cracked everywhere by minor fissures running generally parallel to the main one, though some are at right angles to it. In a few of the little peaks these cracks follow nearly horizontal lines round them, one above another, indicating the probability of a subsidence of the whole mass into the crater at no distant date. Nearly everywhere the regular stratification of the scoria along the margins can be traced, but it is particularly marked in the rounded southern end of this part of the fissure, as illustrated in Plate No. 6.

The surface of the slopes is everywhere composed of fine scoria of a black or reddish-brown colour, intimately mixed with fine pumiceous sand; and scattered over it in great profusion are blocks of trachytic and rhyolitic rock, of sizes varying from a few inches in cubic contents to blocks measuring as much as 250 to 300 cubic feet. Most of these show little or no sign of fusion; but there is one place on the south-east side of the fissure where enormous masses of fused or partly-fused rock (lava, in fact) are to be found. Two pieces of rounded form, containing about 250 cubic feet each, were found partly imbedded in the fine scoria, and these had evidently been ejected after the finer material on which they rested, for in their fall they had excavated dish-like hollows, and broken up other rocks on which they fell. Both were completely molten on the surface. Nor were these the only rocks which showed by their position the date of their ejection. Numbers of others, and many of large size, have certainly been thrown up since the outburst ceased in any force. Several minor outbursts of short duration were witnessed from Rotorua and other places during the first and second weeks after the eruption, and these rocks were doubtless cast out at that time. The Survey party witnessed from below one of these paroxysmal outbursts on the 6th August. Without any warning or noise a vast mass of steam and smoke shot suddenly into the air with great velocity to a height of a thousand feet or more, and gradually rolled away before the wind. It was like the smoke from a gun, and was over directly.^*

The south-eastern side and south-western end are where the native rocks lie in the greatest profusion—so much so that walking becomes difficult. Wherever they are found in the neighbourhood of the cracks which have been referred to they are coloured a bright yellow. These cracks, which may be numbered by the hundred, are of all sizes from a few inches to 20ft. in width, and are sometimes over 100yd. long. They all emit the disagreeable pungent vapour of muriatic acid, and are lined with a most beautiful yellow and green gelatinous matter, probably ferric chloride. One of them on the eastern side, over 100yd. long, 25ft. deep, and 10ft. wide, formed in the rich reddish-coloured scoria, was so thickly covered with this beautiful yellow and green matter, on which the ascending steam had condensed in little drops, as to form one of the most lovely sights possible. The crevice appeared to be lined with exquisite gems, reflecting the rays of the sun in prismatic colours. But this beauty

^* As recently as the 30th October a considerable body of smoke was observed to rise from Wahanga.

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Drawn by G. N. Sturtevant from a photo: by C. Spenser.

Tarawera Fissure,

Shewing old surface of Mountain.

Looking South

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One of the craters in the Great Fissure on top of Ruawahia and Tarawera,

shewing the stratified deposits of scoria and ejected stone; these latter are colored a brilliant yellow by ferric chloride. (Looking South West).

page 49 is very fleeting: the fine yellow colour disappears within a few hours, leaving a rich brown tint on the stones, due, no doubt, to the oxidation of the iron contained in them. The prevailing tint of the scoria is owing to this cause.

When the first clear view of the mountain was obtained a few days after the eruption, the top and sides were seen to be coloured green and yellow, which gave rise to the report that sulphur in great quantities had been deposited there. This appearance was caused by the deposition of ferric chloride in large amount. The colour has since changed to reddish brown. A few minute crystals of sulphur were found in one locality, but only in one.

No sign of any lava-stream having issued from the fissure is to be seen anywhere. Solid lava may be, and probably is to be, found at the bottom of the craters, but at a considerable depth; but it certainly has not flowed out: and therefore those who saw the outburst on the 10th June are mistaken in supposing they saw lava pouring slowly down the mountain-side. The steam or vapour which rises from the craters and the cracks along their margins is that of muriatic acid—its pungent odour is unmistakable; but in some parts a strong smell of iodine was also noticed, and in others an offensive scent like that of burnt leather. As to what this may be, the writer hesitates to offer an opinion.

The escape of vapour, however, is not confined to the fissure or its immediate vicinity: places as far off as half a mile—some near the edge of the plateau—were also emitting steam in small quantities, which seems to indicate that the mountain has been shaken and fractured to its very base, thus allowing the heated vapour to escape by the crevasses formed. This opinion is also supported by the fact of finding the sands at the base of the mountain everywhere warm at 6in. under the surface, even after heavy rains. On the fifth day after the eruption the writer observed with the telescope that after each shock of earthquake—which then occurred hourly—cracks opened on the side and base of the mountain, and at considerable distances from the fissure, from which little jets of steam arose—to disappear, however, after the lapse of a few minutes. Generally the vapour is quite white in colour; but every now and then a jet of reddish-brown smokelike steam is sent up from the craters, and in one or two places steam of a very light-bluish colour was noticed.

At the southern end of the fissure on Mount Tarawera one of the breaks or bridges occurs, where the escaping steam does not appear to have had sufficient power to force an outlet through the rocks of the mountain. The steep slope which this bridge occupies is covered page 50 thickly with rocks of all sizes ejected from the fissure above, the space between being filled up with fine scoria and sand. The latter is, doubtless, derived from Rotomahana and that part of the fissure which lies on the north-east of it. This slope terminates on the perpendicular south-west face of Tarawera. In several places on it steam was escaping on the 28th July, showing that, although unequal to the exertion of opening a great fissure continuously, the eruption has cracked and shaken the underlying rocks sufficiently to allow the steam to reach the surface. The bridge is just a quarter of a mile in width. Its southern end marks the higher edge of the great crater forming the northern termination of the chasm which extends from top to bottom of the south-west side of Tarawera, the depth of which is between 800ft. and 900ft. This depth decreases as the lower end of the chasm is reached, until it finally runs out into the sloping plain lying at the base of the mountain. The western edge is very sharply defined—the rocks falling almost perpendicularly to the bottom—and is, like the fissure on the top of the mountain, a good deal cracked and shaken: the cracks run, however, more at right angles to the chasm than they do above. On the eastern side, nearly half-May down, another crater has been formed, which widens the fissure out somewhat, but its average breadth is about 80yd. Here, again, muriatic-acid fumes are escaping from the cracks, with the yellow ferric-chloride deposits lining them just as above. At the end of July but little activity was shown along this part of the fissure, though every now and then a column of reddish smoke was sent up into the air, but in no great volume. Plates Nos. 7 and 8, taken from below, show the appearance of the chasm.

At the bottom of the chasm another of the bridges occurs, about an eighth of a mile in width, where it is possible to cross the fissure; but immediately below it, and right at the foot of Tarawera, is a circular crater about 120yd. in diameter and 300ft. deep, which was at one time exceedingly active. In July it was quite extinct, and filled with dark-green water, from whence its name, Green Lake Crater. (See Plate No. 7.) It is separated from another crater of smaller size lying to the south-east of it by a sharp wall of rock. In the spot which this latter crater now occupies there formerly existed a rugged mass of rhyolitic rock, separated from the steep sides of Tarawera Mountain by part of the plain, and which from its general likeness to the mountain itself had received the name of "Little Tarawera." Most of this mass of rock has been blown away leaving only small portions of jagged, riven pinnacles to denote its site. It now separates the crater from the new lake formed on its south- page break

Plate No 27.

Drawn by G. N. Sturtevant from a photo: by C. Spenser.

"The Chasm"

in the south-west end of Tarawera Mountain, with Green Lake Crater.

Looking North-East.

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The Chasm.

South-West end of Tarawera

page 51 western side. The immense power of the elastic gases is well shown in this little crater, for scattered around for a considerable distance are huge rocks of rhyolite which have been ejected from it. Many of the rock-fragments about here contain a good deal of obsidian, and some of them small reddish spherulites.

The steep slopes of Tarawera and Ruawahia Mountains, which lie directly under the "mural crown," are covered thickly with fine scoria, which, in many instances, has already become consolidated into a breccia which is difficult and even dangerous to travel over where the inclination is great. The cementing-matter appears to be the very fine sand or mud (or ash) whose origin is probably Rotomahana. The gently-sloping plain south of the foot of Tarawera is thickly covered with this scoria, as are the hills to the east, and where the water has already cut through it and spread it along the channels, it forms a hard stony bed just like the breccias seen in older volcanic formations, which are noted for their hardness and power of resisting atmospheric denudation.

As might naturally be expected from the description of the mountain given above, the nature of the ejecta on and around it are eminently stony. Scoria, black and reddish-brown in colour, generally in a complete state of fusion, forms the bulk; but spread all over and intermixed with it are fragments of the native unfused rock, rhyolitic, trachytic, and perhaps and esitic in character.^* Some particularly interesting specimens of rock in a half-fused state have been preserved, in which the original structure, quite intact, is plainly to be seen; whilst in others the unfused masses are coated with the fused lava. On the top of Tarawera, volcanic bombs may be found, but of no great size; but globular masses as large as a walnut are very common—indeed, remarkably so—on the eastern side of the fissure. They look like grape-shot more than anything else. Newly-formed pumice has undoubtedly been ejected from some of the vents, but in very small quantities. It was only seen by the members of the Survey party on the extreme outskirts of the volcanic deposit, and the amount collected docs not equal more than a handful. Most of the specimens are decidedly different in character from the common pumice of the district, in being heavier and more dense, and of a finer colour. Several specimens are interesting as having adhering to them little flakes of the black scoria of Tarawera, which have served to protect the softer pumice from the attrition to which it

^* The writer makes no pretence to a knowledge of mineralogy, any more than such a rough one as may be gained by the comparison of specimens with the type-rock usually found in every museum.

page 52 must have been subjected when ejected. The character of these flakes of lava would seem to indicate that the pumice came from Tarawera. The presence of this newly-formed pumice, a product of the acidic class of volcanic rocks, in conjunction with the scoria, which, as far as the analysis at the command of the writer goes to prove, belongs to the more basic volcanic rocks—is particularly interesting, and is worthy of careful study by those having a knowledge of mineralogy.^* The sands which are found on the mountain are precisely similar to those which surround Rotomahana crater and the other group of which it is the centre, and are doubtless derived from the same source. It has already been pointed out that Rotomahana was in eruption subsequently to Tarawera, and continued to be so for a more lengthened period, which accounts for the sand being found on top of Tarawera and on its slopes.

Mention has been made of the forests which once clothed the slopes of these mountains: they were of considerable extent, especially on the south-eastern flanks. The eruption has utterly destroyed them over an area of many square miles. They present the most melancholy and desolate aspect: not a green leaf is to be seen anywhere, but, instead, a mass of broken limbs and riven trunks, wrenched and torn to an extent that renders the wood utterly useless. Many of the trees have been burnt, and their charred remains alone are to be seen. The slope now occupied by the chasm on the south-west side of Tarawera was partly under forest formerly, and the trees which covered it suffered in the same manner as the rocks, and have been blown away far and wide over the country. On the southern side of Rotomahana large logs, some as much as 3ft. in diameter by 15ft. and 20ft. long, are found half-buried in the sands, battered and worn, and sodden with water; and these must have come from Tarawera, as there was no other forest in the line of eruption. They have been hurled through the air a distance of four miles. A very striking instance of the force of the wind which accompanied the eruption is exhibited by a totara tree, the stump of which is still standing near the chasm. It protrudes from the ground for about 15ft. or 18ft., and is evidently standing on the spot where it grew: at that height from the ground it is about 8ft. in diameter. The top has been twisted off, and has disappeared, leaving the jagged stump with the splinters all directed in the same way, showing it to have been subjected to a violent wrench. Many other trees (principally rimus) have suffered in a similar manner in the same locality.

Plate No 9.

The New Lake—"Rotomakariri"

Within the Great Fissure-Looking South-west. (From a photo C. Spencer)

The craters and points of eruption which occupy the line of fissure from Wahanga to the base of Tarawera belong to that class which have been described above as characterized by the ejection of molten rock or scoria. But in continuing the description of the fissure towards the south-west we shall deal exclusively—the Black Crater excepted—with the other class, or that in which the ejection of unfused rock, mud, sand, and water predominated. The one class of crater is, strictly speaking, volcanic, the other hydro-thermal (if we give an extended meaning to this term), though undoubtedly the prime cause of action in both is the same. A glance at the map will show that the general character of the fissure changes immediately the base of Tarawera is left: it is no longer the narrow rock-bound rift like that on the mountain, but widens rapidly out into a large crater, or series of craters, through which, however, the narrower fissure can still be traced by the different craters marked on the map. This sudden change in its character is accompanied by a change in the nature of the rocks which have been blown out. The walls and sides of this large area are formed by soft earthy deposits which seem to be lacustrine in their origin, and the stratification of which is nearly horizontal, as may very plainly be seen in the steep cliff forming the eastern side. It naturally offered very much less resistance to the volcanic forces than that of the solid lava of the mountain, and consequently a very much greater amount of material has been removed.

The first point to which attention is drawn is the new lake, called after the smaller one which formerly occupied a position not far from it. This is an entirely new feature, directly due to the eruption. The lake is just one mile long, with an average width of nearly a quarter of a mile. Its eastern side is nearly perpendicular, but the western and higher one slopes much more gradually. In the beginning of August the waters showed signs of ebullition in several places, but very little steam arose therefrom. Its present height is 983ft. above sea-level, or 220ft. below the plain to the east. Plates Nos. 9 and 9A show the lake as seen from the northern end, and on the; eastern or left-hand side can be observed some horizontal lines, the middle one of which denotes the former surface of the country; the recent deposit (there mostly sand) being piled up above it from 30ft. to 50ft. A little stream of water, draining through from the Green Lake Crater, is found at the northern end, whilst at the south-cast side is another of considerable volume, which issues from the bottom of the cliff forming the side of the fissure. The water of the latter is warm, and of an astringent taste: where it leaves the cliff steam page 54 issues in small jets, accompanied by a disagreeable smell as of sulphuretted hydrogen.

The muddy-coloured water of the lake prevents any estimate being formed of the depth, but it is probably not great, and must be decreasing rapidly as the incoherent material on its banks gets washed down by the rains. A few days after the eruption a vast quantity of steam was observed to arise from this locality, and at that time no doubt the fissure was dry; but on the seventh day the steam had entirely ceased, as far, at least, as could be seen from the hills near the Wairoa, and the new lake had probably begun to form in the fissure. It was not, however, until about the 20th July, when Professor Thomas and Mr. Lundius passed round it, that its existence was known. No change had taken place since then up to the date of survey. We can only suppose the origin of this lake to be due to a cessation of activity in this part of the fissure at an early date, which would allow of the falling-in of the sides, aided by the heavy rains early in July, until the lower part of the fissure became completely filled up, thus allowing the waters to accumulate. There is no doubt that a large portion of the drainage of the south and eastern slopes of Tarawera finds its way by subterranean watercourses into it. That large bodies of water have come down from the mountain since the eruption is proved by the width of the watercourses on the plain, and by the great depth (over 100ft.) that a channel leading into the lake lias been excavated quite recently.

The nature of the ejects around the lake is coarse sand and mud, evidently derived from the lake when in a state of activity; but as the steep slope of Tarawera is approached the scoria becomes more and more prevalent, and enormous blocks of stone are found. With a depth of from 30ft. to 40ft. on the shores, it decreases very soon as the lake is left, until at two miles to the east it cannot be more than 2ft. or 4ft. deep, as the stems of the tea-tree are everywhere seen sticking up through it. The surface is capital walking when dry. It is composed of coarse and very fine particles of grey sand, which have a strange power of retaining the water. The coarser particles appear to be loosely cemented together by the finer ones, and in this it differs materially from ordinary sand. After rain it becomes mud, but with no plasticity. It is difficult to say whether it should be called mud or sand: under different circumstances it may be either. As stated previously, the sands are warm 6in. to 10in. under the surface at the base of Tarawera even after heavy rains. This heat may be due partly .to that retained ever since the matter was erupted, or partly to the heat of the underlying rocks. On top page break

Plate No 9A

Drawn by G.N. Sturtevant from a photo: by C. Spencer.

Looking South-West Along Fissure

from Mt. Tarawera.

page 55 of the range of hills westward of the lake, steam in small jets still escapes from the ground in several places, even half a mile off the edge of the lake.

The fissure widens out somewhat suddenly at the south-west end of the lake into an undulating flat, covered with the usual grey sand and mud. The walls on the east are quite perpendicular and about 250ft. high, hut a talus of mud is found along the foot everywhere, and from it oozes out in several places a little cold water, which drains away into a lake shown on the map. On the opposite or western side the bounding hills slope upwards at a very steep inclination. They are indented by three crater-form hollows, from which a large amount of steam arises. The steam issues from a number of funnel-shaped depressions varying in diameter from a few feet up to 30ft. or 40ft. The two little lakelets shown in the line of fissure are both very active along their margins, though the water of the larger one is cold. The western side of the latter is formed by perpendicular rocks, which are cracked and fissured from top to bottom, from out of which the steam issues with great violence, giving rise to a deafening noise, to be heard a long distance off. The crater directly to the west of Star Hill, although small, is very active indeed, and is filled with steam up to its rim—so much so that no sight of the bottom can be obtained. The ridge which extends from the Banded Hill directly towards Star Hill is composed of earthy stratified clays ending abruptly against masses of hard rhyolitic rocks, which form its northern end, just above the lakelet before mentioned. These rocks are also steaming, whilst immediately at their base are several extinct fumaroles, some filled with water, others dry, and near them a strong odour of petroleum is perceptible. This ridge seems to have formed a division in this part of the fissure separating the Rotomakariri series of craters from those of Rotomahana; but in the direct line of fissure it is blown out, and the lakelet occupies that part as a separate crater, now nearly extinct, but which has been exceedingly active, judging from the large amount of rock-fragments scattered about. All over the place just described there are several funnel-shaped depressions marking the sites of fumaroles of various sizes now extinct. The general level of the plain is 980ft. above sea-level, or just 100ft. below the former level of Rotomahana Lake.

If we take the Banded Hill as a natural division of the fissure, it forms the eastern side of the great crater of Rotomahana, which has an east-and-west diameter from there of just one and a half miles, and a north-and-south one of about the same. This gives an area of page 56 slightly over two square miles as the size of the crater, which is surrounded by precipitous and in some places perpendicular walls, varying from 200ft. to 300ft. in depth. Below the walls the ground slopes by ridges and hollows to the central cavity, now filled by water. The height of this above sea-level is 565ft., or 515ft. below the former level of Rotomahana Lake. It will be seen from the map that the elongated lake or pool at the bottom of the crater occupies the line of the great fissure. The water is evidently hot, though none of the Survey party descended to it to ascertain the fact, the danger at that time being too great from the clouds of scalding steam which obscured a large portion of the crater. It is but a moderate estimate to assume that the depth of solid matter which has been removed from the crater by the eruption is 300ft.; but this will give a quantity equal to nearly 620 million cubic yards. In other words, it would cover two hundred square miles a yard in depth.

At the end of July and beginning of August the principal foci of activity within the crater were distributed along the line of fissure, and around the west, north, and eastern sides, though nearly everywhere, whenever the dense cloud of steam admitted of a sight, fumaroles and points of activity could be discerned in countless numbers covering other parts of the sloping bottom. The southern "hay" had ceased to be active, except in a few places where steam issued from the sides of the little river draining down into the central lake. This river was hot—indeed, almost boiling—where it issued from the ground, which it did with great noise and volume, its waters so strongly impregnated with iron as to colour the rocks with a bright-yellow ochreous deposit, though the water was quite clear. It is believed that this "boiling river" was one of the subterranean feeders of Rotomahana. It derives its waters from the drainage of the plain above and probably also from Rerewhakaitu Lake and the slopes of Tarawera. The heat of the waters will arise from the same source as that which caused the excavation of the crater. The signs of recent great activity in the southern bay are exhibited in a striking manner. Huge rocks and masses of earth have been hurled and tumbled about in the most extraordinary manner, giving the place the appearance of having been the scene of sluicing operations on a most gigantic scale. Numbers of funnel-shaped depressions of all sizes up to 30ft. or 40ft. in diameter indicate the positions of the steam-vents which caused the havoc that has been wrought, though all are now extinct. No molten rock is to be seen anywhere—nothing but the native rock—that is, the earthy deposit which forms the basin of Rotomahana, and some of the harder trachytic or rhyolitic rocks, and these are half-buried in the grey- page break

The Steam Cloud of Rotomahana from te Hape o Toroa hill.

(Looking North East) As seen in June 1886

From a photograph by C. Spencer.

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Plan No. 3

page 58 Directly to the south-west of the crater is Te Hape o Toroa Hill, 1,940ft. above sea-level; and from a point on its side 1,800ft. above the sea the best view of Rotomahana is obtained. The following quotation from the writer's first report^* describes the appearance of the crater on the fifth day after the eruption: "The Pink Terraces were in such a situation as to be at least a quarter of a mile within the margin of the present crater, and no eye can penetrate through the dense mass of steam to ascertain their fate. Occasional breaks in this dense veil allow of momentary glances into the crater, but for no great distance, and the sight disclosed is one of horror. A dim brownish twilight, making everything of a hideous hue, enables one to sec a dreadful mass of boiling mud, black and brown in colour, with seething pools of steaming water or liquid mud, sometimes cast up into fumaroles ejecting steam, at others vomiting forth stones and mud with a noise like the roar of innumerable steam-engines. From time to time the more active vents along the margins, after a prolonged roar, or a sharper detonation like that of a cannon, shoot forth high into the air large bodies of stones, sand, and mud, which generally fall back again from whence they came; at other times they are scattered far and wide over the mud-covered hills around the margin, the stones leaving dish-like hollows where they disappear beneath the surface. The outer edge of the crater differs in height above the bottom according to position, and no general statement could be given as to an average height; but at the west side it is probably about 300ft., the upper part being formed of debris thrown out from the crater. To the margin of this ejected matter it is dangerous to approach: it is constantly falling in, and is full of cracks for many yards back. To the east of Te Hape o Toroa, along the valley which was formerly occupied by a stream running into Rotomahana, are several points of eruption (see Plate No. 10A, where a few of them are shown), some of them throwing up stones and mud at intervals, generally preceded by a loud detonation. The top of this hill, being about a quarter of a mile from the margin of the crater, affords an excellent view of the whole eruption; but, at the same time, the frequent earthquakes tend to engender a feeling of insecurity, and a wondering feat lest the whole steep hill-side should subside into the crater below." At that period the stones were frequently ejected from the

^* Appendix to Journal, House of Representatives, H.-26, 1886. The writer is glad to have this opportunity of correcting the only serious mistake which later explorations prove to have occurred in that report. It was there stated that only some doubtful specimens of fused rock had been met with: the fact is, the molten matter was covered up by the later ejection of sand, mud, and ashes, and it was only after the first rains that it appeared everywhere. Tarawera at that time was unapproachable.

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Part of Rotomahana Lake, under Te Hapehill.

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Plate No 11

Drawn by G.N Sturtevant from a Photo by C.Spencer

Former Outlet to Rotomahana

now filled in with sand etc.

page 60 and distinct craters, all of which are blown through the solid rock, and are at the present time filled with hot water. The two northern ones of the group were nearly extinct in the beginning of August, but the others were intermittently active, especially so the Black Crater, a name derived from the colour of the ejecta. (See Plate 12A, and also 14B, which shows the interior of the crater as blown out from the solid rock.)

An attempt has been made in previous pages to show that, the origin of the eruption is deep-seated; and some evidence of this is demonstrable from the position the fissure here occupies with respect to the original valleys and hills. It will be seen from the map that from the south end of the Echo Lake Crater a valley, varying from 300ft. to 400ft. deep, runs, parallel and quite close to the fissure, right down to Rotomahana Crater—for a distance of over a mile. Now, had the eruption been in any sense superficial, this valley, offering the least line of resistance, and quite close to the general direction of the fissure, would be the line which it would naturally be expected to take. But, instead of this, we find that spur after spur has been severed, and the straight line of fissure continued quite irrespective of the formation of the country. Plate No. 13 illustrates this well. The crater there shown is blown out of one of the steep spurs coming down from Te Hape o Toroa, whilst the deep valley on the left, of the picture is left intact. Indeed, the explosive forces seem to have had, as it were, a preference for the spurs and hills rather than the lower intervening ground, for all of the five southern craters occupy the tops of the hills, excepting part of the Echo Lake Crater, which cuts right across a former valley.

The Black Crater, though small in size, has been, and still is, one of the most active along the whole line. When first seen, on the fifth day after the eruption, it presented a most beautiful sight: the vast column of steam that shot up into the air with great velocity, nearly as high as that from Rotomahana (15,400ft., as measured), was accompanied by constant paroxysmal discharges of rock and mud, which rose in a pyramidal form to a height of from 500ft. to 600ft. above the bottom of the crater. There appeared to be alternating ejections, first from one end, then from the other; and frequently the direction of the outburst deviated from the perpendicular, and the stones then shot out in a curve, falling on the exterior slopes of the hill with a noise like the rattle of musketry. The stones lay smoking on the surface for some time after their ejection. (Sec Plates Nos. 14, 14A, and 14C.) The activity has a good deal subsided now, but an eruption took place on the 4th August—only lasting a few moments, how- page break

From a photograph by J. C. Blythe.

From, foot of Hape o toroa hill looking South to Kakaramea, across "Black," "Echo," and Southern Graters.

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Plate No 13

Crater North of Black Crater

shewing how fissure has cut through the spurs of Hapeo-Toroa Hill.

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The Fissure from Top of Black Crater,

Looking Across Rotomahana to Tarawera in a North-East Direction.

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Plate No 14

The Black Crater in Eruption

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View from Pareheru on June 19^th 1886.

Black Crater in eruption.

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Interior of part of the Black Crater.

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The Black Crater.

From the West.

Illusrates pit-marked appearance of the hills where stone have been ejected and sunk in.

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General View of Craters.

From a photograph by C. Spencer.

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The Fissure,

Looking Across Echo Lake and Inferno Craters in a North-East Direction.

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Echo Lake Oraler looking North East.

Shewing the large amount of ejected stone on the left; also the [unclear: center] in the side of hill called Gate of the [unclear: Inferno].

page 61 ever—when stones and mud were thrown out. The next to the south is the Inferno Crater, which occupies the side of the hill sloping down from the Black Crater. It is in appearance like some enormous gateway leading to the nether regions. Little information can he gained, however, as to its features, for the dense mass of steam which arises from it obscures everything but part of the great boiling pool in the bottom and the black perpendicular rocks forming its sides.

Reference was made on page 45 to the exception which the Black Crater offered to the general character of the southern part of the fissure. This exception consists in the fact of it and the Inferno having ejected molten rock of the same composition as that from Tarawera. The walls of the Inferno present the same appearance as the fissure on Tarawera—that is, the rock appears to have been subject to heat sufficient to partly fuse it. Several small volcanic bombs and a large number of rudely spherical masses of molten rock have been picked up in this locality, though nowhere else except on the mountains. These fusea globular masses vary in size from that of a walnut up to 4in. or 5in. in diameter; they are heavy and solid, and rarely scoriaceous.

The Echo Lake Crater, which lies immediately to the south of the Inferno, is divided from it by a low ridge about 50yd. wide. It is rather more than a quarter of a mile long, with an average width of 120yd. It has nearly perpendicular cliffs for most of its circumference, but at the north end these fall away to the level of the lake which now occupies the basin. In the beginning of August it had ceased to be very active, though the water was boiling here and there, and steam rose from the surface everywhere. Plates Nos. 15 and 16 give a good idea of its appearance as seen from the Southern Crater. The channel which leads away from the north-east end of this crater is now dry; but when Professor Thomas and Mr. Lundius passed along here in the middle of July, a large stream of very hot water was flowing from the crater-lake down towards Rotomahana. Where it leaves the crater the channel is about 20yd. wide, but it rapidly widens out to 120yd., and its bed is strewn with great rocks ejected from one of the adjacent craters. The rocks on the western side of the crater appear to be very solid below, and from fissures in them the steam still escapes. The mass of rock through which the crater has been blown out appears to be a hard, dense, banded sandstone of volcanic origin; in some specimens the bands or lamina; are highly coloured—green, red, and brown being the predominating tints. This crater (or craters, for there are probably two) has been page 62 the scene of explosions on a large scale, if we may judge from the immense number of rocks scattered around it, some of which are very large—as much, indeed, as a thousand cubic feet in solid contents. The floor of the valley to the east of it is strewn with ejected rocks in a remarkable manner: they are piled up in such a way as to lead to the belief that a continuous and heavy discharge took place in this particular direction for a considerable time; and, as they are not covered with the lighter ash and sand, they must be the result of the latest effort of the crater. Nowhere along the whole fissure are such numbers and varieties of unfused rocks to be found. The mineralogist will here find, over the space of six or eight acres, a complete museum of volcanic rocks. Although the east side is that on which the greatest number of rocks is found, all the hills and gullies for a considerable distance round are thickly dotted with them, either lying on the surface or buried under the cup-shaped depressions which characterize the hills. One of these hollows measured 30ft. in diameter by 12ft. deep, denoting where a rock larger than usual had sunk out of sight. The sand and ash on the edges of the crater is about from 15ft. to 20ft. in thickness. Plate No. 15 shows the old and new surfaces plainly.

To the south of the Echo Lake, and separated from it by a valley, is the Southern Crater, the dimensions of which are 200yd. long by 100yd. wide, and with a depth of 350ft. below the crateredge. On the fifth day after the eruption this was still very active, though filled with boiling water. An enormous column of steam arose from it high into the air, and obscured the surface of the water. The crater is blown out of a ridge, valleys dividing it, on the north from the Echo Lake Crater, and from the next ridge to the south. In neither of these valleys can the fissure be traced. It is somewhat remarkable that no sign of the fissure is to be observed south of the Southern Crater: not even a crack can be seen; but it is quite possible that the thick covering of ash hides any minor fissures or earthquake-cracks in this locality, whilst they are to be seen some distance south-westward. Plate No. 16c shows the nature of the country southwest of the Southern Crater, and in continuation of the line of fissure.

The nature of the deposit covering the country round the southern-most craters differs somewhat from that round Rotomahana: we no longer have the surface of sands and mud, which, acted on by the rain, forms deep furrows lying closely together (see Plate No. 17), but a fine impalpable powder of the consistency of flour, of the same colour and appearance as Portland cement. It docs not cut up into page break

Stones S.E. Side of Echo Lake.

From, a photograph by J. C. Blythe, Nov 1886.

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Plate No 15B.

The Southern Crater.

Looking North-East along Fissure.

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Echo Lake from the Southern Grater.

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From Kakaramea Mt. (9mos before eruption).

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From, Kakaramea Mt. looking across Line of eruption).

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South West from Hape o Toroa.

Looking along country in the direction the great fissure would eoctend, if produced.

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Shewing appearance of mud covered hills east of Rotomakariri, and the deeply furrowed surface due to rain water

page 63 little channels as the sand and mud does, but still envelopes the hills much as it did when first ejected. Doubtless it owes its origin to the southern craters, and is probably of later date than the ejecta from Rotomahana. In some places where it could be observed in the beginning of August it was found to be quite dry at 3ft. under the surface, notwithstanding that very heavy rains had fallen since the date of the eruption. The base of the Hape-o-Toroa Hill is its northern termination, whilst it extends in a southerly direction to half-way up Maungakakaramea Mountain, where when first seen it appeared to end quite suddenly, the lower part of the hill being quite white, as if covered with snow, whilst the upper showed the native vegetation of fern and tea-tree apparently uninjured. The western edge of the deposit at Pareheru Bush is almost equally well marked. Here it fell among the clumps of bush there growing, and has left them scorched and dying, showing that it fell quite hot: indeed, five days after the eruption it was quite warm 6in. under the surface. After heavy rain it forms a mud of the most tenacious and plastic character. Few who have travelled over it in that state will ever forget the fatigue it gave rise to. If moulded when in the wet state it dries quite hard, like cement. Scattered through it, but in no great quantity, is a little fine scoria, evidently derived from Tarawera; hut this is only found a little way under the surface. Outside the hounds of this ash, (if ash it may be called, for the name seems somewhat of a misnomer) a little scoria or lapilli is found to extend for a mile or more, but in very small quantities.

No doubt Scrope is correct in assigning a sudden explosion as the cause of these and similar craters. After a few years, when the rains shall have washed the recent deposits off the hills, and the vegetation again appears near the southern craters, there will be little left to denote the origin of them but the blocks of unfused rocks which lie scattered around.

It seems very probable that Rotokawau, the beautiful little lake, encircled with perpendicular cliffs, which lies near Tikitere, close to the shores of Rotorua, is another of these craters due to a sudden explosive effort unaccompanied by the ejection of lava or scoria. It page break

Plate No 18.

Tarawera Mountain

From above Te Ariki. Shewing position of "The Chasm"

page 65 has been blown through a rhyolitic tuff or lava flow now covered with a growth of tall forest trees, and still has a small but active fumarole on its western edge.