14 



NA TURE 



[May i, 1884 



Sunda, and destroyed a number of kampoengs and more 

 than 35,000 lives. 



There is much uncertainty about the time at which 

 these waves originated, and this is not surprising. The 

 number of Europeans who witnessed the catastrophe on 

 the coast places in the Sunda Straits and on board ships 

 was but small ; besides, most of them were in a state of 

 great alarm, so that observations with a timepiece were 

 exceptional. Most of the estimates of time were no more 

 than a rough calculation, which, especially after the dark- 

 ness set in, were not very trustworthy. This explains 

 what came under my notice, that a time computation of 

 the same event in the same place by two different people 

 showed a discrepancy of an hour and a half. 



Besides, a remarkable fact must be taken into account, 

 namely, that the largest wave, the only one which spread 

 great distances along the north coast of Java and to the 

 south-west, and which surpassed all other waves by far in 

 height, was almost seen nowhere ; at Tjiringin alone this wave 

 was seen to approach before the darkness began, and this 

 was about ten o'clock on the morning of the 27th. Anjer 

 was already destroyed at 6 a.m., and then abandoned. 

 At Telok Betong, and in the lighthouses on the Vlakken 

 Hoek, and at Java's First Point, the wave was not seen 

 because it was pitch dark. Even in the lighthouse, 40 

 metres above the sea on Java's First Point, nothing was 

 seen of the wave, and the destruction of the coast country 

 was only discovered the next morning when it became 

 light. 



As the great darkness at Bantam set in soon after the 

 great detonation of ioh. 5m. — the same explosion which 

 gave rise to the great airwave — and as the wave had onlj 

 time, before the darkness set in, to reach the neighbour- 

 ing Tjiringin, which lies 47 kilometres from Krakatoa, 

 this tide wave cannot have arisen much before 9h. 50m. 

 or 9h. 55m. At the Vlakken Hoek, 103 kilometres from 

 Krakatoa, it appeared at about ioh. 30m., which agrees 

 with our time computation, if it be taken into account 

 that the velocity of the waves towards the Vlakken Hoek 

 must have been greater on account of the greater depth 

 of the sea than towards Tjiringin. 



It is very probable that shortly before ten o'clock a 

 subsidence of the hollow crater walls of one or both of 

 the active craters took place, that through this the water 

 gained access in large quantities, and that then half of 

 the peak, which had been previously undermined and 

 fractured by /he eruptions, also disappeared in the depths. 

 The cause of the great wave motion must no doubt be 

 sought for in the subsidence of the peak. Of the northern 

 part of the island, after the many eruptions, not much 

 more than a hollow shell can have remained, the subsi- 

 dence of which could not have caused waves of great 

 importance ; nor could the rush of the water produce 

 great waves, but rather a suction towards Krakatoa, and 

 this may be the cause of the water on the coast first 

 retreating in various places before the great flood 



I'. 1 need. 



The peak itself, however, was still massive, and I have 

 calculated that the part which fell of this mountain alone, 

 without Danan and Perboewatan, possessed a volume of at 

 least I cubic kilometre. If this cubic kilometre be sud- 

 denly plunged into the sea, the same quantity of water 

 must be displaced, which must give rise to a circular wave 

 round Krakatoa. 



There have been, however, other smaller waves : 

 one as early as Sunday evening, August 26, at 5I1. or 

 5I1. 30m., two more in the night, and on Monday 

 morning at 6h. a wave which destroyed Anjer. It is 

 difficult to account for the small waves by assuming that 

 parts of the mountain gave way, because, if so, probably 

 the sea would have gained access also, and mud eruptions 

 would have occurred much sooner, unless it be supposed 

 that mud was ejected, but nowhere far enough to reach 

 inhabited places, winch i^ not quite impossible. 



If no subsidences of the mountain had yet taken place, 

 there only remains the assumption that these waves were 

 caused by the enormous masses of ejected matter falling 

 into the sea. As has been said above, 12 cubic kilometres 

 of stones and ashes are lying close round Krakatoa ; this 

 quantity has been thrown there from May 20, but cer- 

 tainly, for the greater part, during the violent explosions 

 of August 26 and 27. Assuming that, for instance, about 

 1 cubic kilometre of these substances was thrown into 

 the sea at a time, waves must of course have been the 

 result, which, as I have calculated, must have reached a 

 considerable height. 



The large wave of ten o'clock specially ran up a great 

 height against the precipitous cliffs of the Sunda Straits, 

 according to our measurements as follows: — 15 metres 

 up the lighthouse at the Vlakken Hoek ; at Beneawang 

 (Semangka), uncertain ; at Telok Betong, before the house 

 of the Resident, 22 metres ; at the Apenberg (Goenoeng 

 Koenjit), 24 metres ; at Kalianda, up a sloping plain, 24 

 metres ; on the south side of Thwart the Way, ± 35 metres 

 (not measured) ; on the south side of Toppershoedje, 30, 

 on the north side, 24 metres ; at Merak itself the height 

 cannot be ascertained with certainty, the old house of the 

 engineer stood only 14 metres above the sea ; about 2 

 kilometres south of Merak, 35 metres ; north of Anjer, 

 on the coast opposite Brabandshoedje, 36 metres. The 

 height, therefore, varies everywhere, and depends on the 

 situation of the places, their distance from Krakatoa, 

 their being more or less sheltered, and the steepness of 

 the coast. At Sebesi there is no trace left of the tide 

 wave, as everything is thickly covered with ashes, which 

 fell after the wave. At Seboekoe the height amounts 

 from 25 to 30 metres, but no measurement was taken. 



The big wave which was propelled from Krakatoa at 

 about 9V1. 50m. spread over great distances, among others 

 as far as Ceylon, Aden, Mauritius, Port Elizabeth in South 

 Africa, and even to the coast of France. The velocity of 

 the waves varies greatly, of course, since it increases with 

 the depth of the sea ; I shall not be able to give a de- 

 tailed summary till the tables of all the self-registering 

 tide apparatus shall have been collected. For the 

 Indian Archipelago, and a few points beyond, I found the 

 following numbers : — 



,. , . Average .lepth 



Places , X '' °? lty P, Cr of ihe sea in 



lloul ln m,,es iretres 



Island Noordwachter 

 Tandjong-Priok (Batavia) 

 Undeepwater Island 

 Dendang (Billiton) 

 Tandjong-Pandan (Billiton) ... 

 Tjilamaja (Krawang) ... 

 Oedjoeng Pangka (near Soerabaja) 

 Pasar Manna (Benkoclen) 



Padang 



Mauritius (Port Louis)... 

 Port Elizabeth ... 



In our Archipelago the velocity is small, owing to the 

 shallowness of the sea, but in the deep sea, on the route to 

 Mauritius and the Cape, it increases considerably, i.e. 

 amounts to more than 300 knots an hour, a velocity which 

 is alone to be compared to that of the lunar tide wave and 

 the earthquake waves of Simoda, in Japan, of December 

 23, 1854, and of Tacna, in Peru, of August 13, 1868. 



From the velocity of the wave the average depth of 

 the sea between the places along its path can be deter- 

 mined ; I have put together in the foregoing table those 

 various degrees of velocity, but they can only be trusted 

 when the height of the wave is small with respect to the 

 depth of the sea, which in our Archipelago is not strictly 

 the case. However the numbers agree pretty well with 

 the sea-chart. In the time computation of Mauritius 

 there appears to be a mistake, as the average depth can- 

 not be so different from that of Port Elizabeth. 



After these terrible events Krakatoa slowly calmed 



