May i, 1884] 



NA TURE 



tahedra, as the oldest component part. The quantity 

 of magnetite decreases in the ashes in proportion as they 

 fell further from Krakatoa. 



If the molten mass had slowly cooled, an ordinary 

 augite-andesite or andesite-steatite (with rhombic pyrox- 

 ene), would have originated. 



The thickness of the ejected substances diminishes on 

 the whole as the distance from Krakatoa increases ; the 

 coarser material fell principally within a circle, with a 

 radius of 15 kilometres drawn round Krakatoa, although 

 pieces of the size of a fist were still thrown at a 

 distance of 40 kilometres. Within the circle of 15 

 kilometres' radius the thickness of the layers of volcanic 

 substances is 20 to 40 metres. At the back of the Island of 

 Krakatoa, the thickness of the ash mountains at the base 

 is in some places even 60 to So metres, but diminishes in 

 thickness upwards, so that, in the deep clefts, which have 

 already been hollowed out by the water, the old surface 

 of the mountain and the fallen trees appear. 



The thick layers of ashes were cooled at the top at the 

 time of my visit, but were still very hot below, so that in 

 the deep ravines hot water and steam appeared every- 

 where ; also at Verlaten Island, Long Island, the Islands 

 Steers and Cahneyer, and even at Sebesi, steam was seen 

 to escape here and there. At Krakatoa there are, besides, 

 stems of trees which have been carbonised by the hot 

 ashes and continue to smoulder close to the fracture, 

 where the air can penetrate, so that at night a little fire- 

 glow and smoke may be observed. These small fires 

 specially gave rise to the report that Krakatoa was still 

 active. 



The ascent of the mountain from behind, on the pumice- 

 stone elevations, is difficult, but possible ; the innumerable 

 crevices, into which one must constantly descend, make 

 the climbing up in the great heat and the total want 

 of shade very fatiguing. The ascent may be made from 

 the northwest, close along the rupture till about 20 metres 

 from the top, which, according to our measurements, lies 

 831 metres above the sea ; the surroundings of the top 

 are rent and constantly crumbling away. 



Between Krakatoa and Sebesi there is a large quantity 

 of ashes and pumice-stone which has filled up that entire 

 part of the sea, and projects in two places above the sur- 

 face. To these two points the names of Steers Island 

 and Cahneyer Island have been given. They do not rise 

 more than a few metres above the sea, have much to 

 suffer from the beating of the waves as they only consist 

 of loose material, and will soon be washed away. The 

 sixteen small craters between Sebesi and Krakatoa, re- 

 duced in later reports to six or four, have never existed. 

 The smoking volcanic accumulations have been mistaken 

 for active craters which, at first, from a distance was not 

 unlikely to happen. 



The finer ashes were blown eastward (east-south-east), 

 to near Bandoeng (250 kilometres from Krakatoa), in a 

 north-north-west direction to Singapore and Bancalis, 

 respectively 835 and 915 kilometres from Krakatoa, in a 

 south-west direction as far as Kokos Island (Keeling 

 Island), 1,200 kilometres from Krakatoa ; how far the 

 ashes were projected west, north, and south is unknown ; 

 the surface comprises at least 750,000 square kilometres, 

 that is, almost as large an area as Sweden and Norway, 

 larger than the Austro- Hungarian Empire, also larger 

 than the German Empire with Denmark (including 

 Iceland), the Netherlands, and Belgium together, and 

 twenty-one times the size of the Netherlands. 



Evidently the prevailing wind-currents, i.e. south-east 

 and north-east, have carried the particles along, which 

 causes the outline of the surface covered with ashes to be 

 irregularly curved. 



Finer particles still have fallen even beyond this line 

 into the sea, as appears from reports of ships ; and the 

 finest of all, mixed with a quantity of vapour, remained 

 a long time floating in the upper air-currents, and, pro- 



pelled by the wind, have made a journey round the world. 

 The vapour was condensed to water, and froze in the 

 cold currents ; the refraction through the innumerable ice 

 crystals caused the beautiful dark red glow which was 

 observed the List months in so many places in Asia, 

 Africa, Europe, and America ; while the ash particles 

 partly obscured the sunlight, or gave the sun blue and 

 green tints at its rise and setting. 



If one considers that the volume of the solid ejected 

 substances already amounts to several cubic kilometres, 

 and that the volume of ejected gas substances was per 

 haps hundreds of times as large, the hypothesis of a 

 cosmic ice cloud to explain the air phenomena seems to 

 me quite superfluous. 



That the ash particles, as a matter of fact, were carried 

 very far in the upper air-currents, has already appeared 

 from snow which fell in Spain, and rain in the Nether- 

 lands, in which the same components were found as in the 

 ashes of Krakatoa ; and that the particles must moreover 

 have been projected very high at the last eruption may 

 be concluded from the report that, on the 20th May, 

 during one of the first eruptions, the steam cloud — accord- 

 ing to the measurements taken on board of the German 

 man-of-war, Elisabeth, which left Anjer that morning at 

 nine o'clock— must have reached a height of at least 

 1 1,000 metres. During the much more violent explosions 

 of August 26 and 27, the height, if the above report 

 may be relied on, may very well have reached 1 5 to 20 

 kilometres. 



I found that on calculating as accurately as possible the 

 quantity of ejected solid substances, they reached iS 

 cubic kilometres. In doubtful cases the lowest figure was 

 always selected, so that 18 kilometres may be too low, 

 but not too high, a computation. The possible margin 

 amounts in my estimation to not more than 2 or 3 cubic 

 kilometres. 



However large a quantity this may be, it does not 

 nearly reach that which the Tombora produced in 1815, 

 and which Junghuhn estimates at 317 cubic kilometres ; 

 this computation, however, rests on but few data, so that 

 in my opinion a quantity of 150 to 200 cubic kilometres 

 will come nearer the truth. But even in that case the 

 number is eight to eleven times larger than ours, which is 

 not astonishing, as at that time at Madura, a distance 

 of more than 500 kilometres from the Tombora, the sun 

 was totally obscured/^;- three days, whereas the darkness 

 here only lasted a few hours. 



Of these 18 cubic kilometres, which represent a weight ot 

 more than 36 X io 12 kilogrammes, no less than 12 cubic 

 kilometres, or two-thirds of the whole ejected quantity lies 

 within the circle with a radius of 15 kilometres drawn 

 round Krakatoa. As the sea between Krakatoa and 

 Sebesi was not deeper than 36 metres, and the thickness 

 of the volcanic ejections amounts to almost the same, the 

 navigation there has become quite impossible. A little 

 further the thickness diminishes considerably. From 15 

 to 12\ kilometres from Krakatoa, the average thickness 

 amounts to no more than 1 to iA kilometres ; within this 

 ring lies Sebesi, which now only presents a heap of 

 ashes, with a few projecting stumps of trees ; nothing 

 here remains of the four populated kampoengs which 

 formerly stood on the plain opposite the small island 

 Mengoenang (Huisman's Island), all has been washed 

 away, and is covered with a layer of ashes 1 metre thick. 

 From 22i to 40 kilometres, the average thickness of the 

 ashes amounts to 0'3 metre, then to 50 kilometres 02 

 metre. At a still greater distance from Krakatoa the 

 thickness speedily diminishes to 2, 1, and half a centimetre, 

 but the finer the ashes become the more the direction ot 

 the wind is perceptible. An "ash map " will be added to 

 the detailed report. 



One more -very remarkable phenomenon during the 

 eruption was the formation of powerful sea waves, which 

 flowed over the low-lying coast districts of the Straits o! 



