21 



eruption the original soil was found to lie locally bare in the eroded 

 ravines 1). 



A thin covering, lasting no more (and probably rather less) than 

 2 months, may have destroyed many superterranean organisms, but 

 must be considered insufficient to kill all deeply buried rhizomes, 

 roots, seeds, spores, mycelia and bacteria, unless it can be proven 

 that it has strongly heated the underground to a considerable depth 

 and during a long time. 



But for the thmly covered higher areas on the south- and south- 

 eastern sides this proof has not been given. During the first years 

 after the eruption the temperature of the underground was never 

 measured -). In 1883 no lava has flown out and the locally thin, layer 

 of ashes and fine grit need not at all to have been very hot. The 

 products ejected by the crater, active in 1883, 1 recall to memory 

 that the crater in the Rakata-cone itself remained inactive , possessed 

 during the catastrophe an initial speed 3 ) of more than 1000 m. per 

 second. As the active crater lay far beneath the top of the Rakata- 

 cone on its northern side and at a distance of but a few km., only such 

 eruptive products as were almost vertically ejected could fall down 

 on the sKSfee^side of the cone; the other ones must have been hurled 

 far beyond it. The materials which were thrown up almost vertically 

 must have reached a very considerable height, partly of 50 km. and 

 more '*), and thereby very cold zones of the atmosphere. The mean 

 air-temperature ^J in the Dutch Indies at 5 km. above sea-level is 

 -1,5 C, at 10 km. -34 C, at 15 km. -74 C, at 20km. -80 C. 

 Upwards of 20 km. the temperature is somewhat higher but remains 

 still very low. At 30 km. it is -55 C and at 50 km. probably as 

 muchr Above 30 km. there are strong air-currents which, during the 

 eruption, must have had a speed of 30 m. per second. This speed is, 

 at this altitude, in the latest years also observed by means of pilot- 

 balloons. 



The ashes and the fine grit which reached a greater height 



1) Verbeek, Kort Verslag (1884), p . 13.-J<rakatau (1888) p . 122 In 1908 (| a ar- 

 verslag Topogr. Dienst Ned. -Indie 1908, p 157) Fransen Herderschee found at 

 a low altitude a ravine with a rocky bottom, which made the impression to be an 

 old lavastream and afterwards, beneath an altitude of 300 m. another ravine the 

 bottom of which was formed by the original rock-formation, the old mantle of the 

 volcano. In 1916 De longh (laarboek van het Mijnwezen in Nederlandsch Oost-lndie 

 1916, p. 43) stated that a not unimportant part of Krakatau was deprived of its tuff- 

 mantle and exhibited the original surface of the cone. 



2) Verbeek, by letter dated April 25th 1922. 



3 ) Verbeek, Krakatau, Dutch Edition (1888), p. 123. 

 *) Verbeek, Krakatau, Dutch Edition (1888), p . 123. 



8 ) Communicated to me by letter of Dr Boerema, subdirector of the Mete- 

 orological Observatory of Weltevreden (Batavia). 



