March, 1913. 



KNOWLEDGE. 



95 



The earliest known eruptions of the Asama-yama 

 occurred in the years 685 and 1108. For this 

 period of its history the chronicle is obviously 

 incomplete. With the year 1527, the eruptions 

 were renewed, and at the same time the record 

 becomes less imperfect. The eruptions occurred in 

 groups separated by intervals of repose. From 

 1527 to 1532 there were three eruptions, from 1596 

 to 1605 four, from 1644 to 1669 twenty, from 1704 

 to 1733 sixteen, from 1754 to 1783 five, and from 

 1803 to 1889 there were nine eruptions. 



Of these fifty-nine eruptions, the greatest was that 

 which occurred in 1783, the year of the great 

 Calabrian earthquakes. This eruption, which lasted 

 altogether for eighty-eight days, began on May 9th. 

 For some time it consisted mainly of loud detona- 

 tions, occasionally accompanied by strong explosions. 

 But these were by no means continuous, there being 

 intervals of quiet, one of which lasted for nearly 

 three weeks. On June 28th, the explosions became 

 more violent. A month later, ashes fell in Yedo 

 (now Tokyo, eighty-five miles distant), where the 

 people, not knowing the cause, wondered why houses 

 and doors were shaken while the ground remained 

 quiet. On August 2nd, the violence of the 

 explosions reached its maximum, large quantities of 

 red-hot stones and sand were projected from the 

 crater. On the 4th, the rain of ashes was so dense 

 that, even in distant towns, lanterns were used 

 during the daytime in the streets. The next day, 

 the eruption attained its climax. In the morning, 

 after many violent explosions, a huge mass of molten 

 lava and hot mud broke through the north wall of 

 the crater and flowed rapidly down the northern 

 flank of the volcano. This lava, after the lapse of 

 more than a century, is still fresh in appearance ; 

 there are few signs of weathering, no vegetation 

 covers it, and the rock still preserves the fantastic 

 shapes into which it was thrown at the time. The 

 total volume of this lava is about one-fourteenth of 

 a cubic mile, or thirty times that of the present 

 crater of the Asama-yama. 



The lava-stream, however, stopped short of the 

 villages, and, therefore, caused no loss of life or 

 property. The great torrent of volcanic mud was 

 more destructive. Descending with a velocity, 

 which at first was not less than sixty miles an hour, 

 it swept down the ravines and overwhelmed the 

 villages along its course, the loss of life rising as 

 high as eighty per cent, of their inhabitants, and 

 amounting altogether to that of one thousand one 

 hundred and sixty-two persons. 



Professor Omori estimates that the district covered 

 by the ashes is about one hundred and forty miles 

 in length, sixty-two miles in width, and not less than 

 four hundred and twenty-five square miles in area. 

 As the layer of ashes was five or six inches deep at 

 a distance of thirty miles, diminishing to one inch 

 at Tokyo, the total volume of the ashes ejected, 

 quite apart from that of the lava and volcanic mud, 

 must have amounted to one-sixth of a cubic mile, or 

 at least sixty times the volume of the present crater. 



The disastrous effects of this eruption are con- 

 nected by Professor Omori with the long period of 

 quiescence which preceded it. For fifty years 

 previously, the calm was broken only by a few small 

 explosions. During the last two or three years of 

 this period, smoke entirely ceased to issue from the 

 crater, the floor of which was gradually raised almost 

 to the level of the crater rim. It was due to the 

 shallowness of the crater in its final stage that the 

 immense mass of lava and volcanic mud broke 

 through the containing wall and flooded the 

 surrounding country. 



For more than a century after this great outburst 

 the Asama-yama remained almost undisturbed. In 

 1803, there were three slight eruptions, followed by 

 others in the years 1815, 1866, 1869, 1875, 1879, 

 and 1889, altogether nine eruptions, none of much 

 account. Since the latter year, however, they have 

 greatly increased in frequency. In 1894, six 

 eruptions took place : in 1899, four ; in 1900, seven ; 

 in 1901, six; in 1902-1907, six more; in 1908, five; 

 in 1909, seven : and in 1910, ten. In the following 

 year, 1911, there were no fewer than forty eruptions, 

 all but three within the first four months of the year. 

 In these estimates, minor detonations and explosions 

 are omitted. Of the sixty-two eruptions during the 

 four years 1908-1911, there were four of considerable 

 strength, namely, those of May 31st and December 

 7th, 1909, December 2nd, 1910, and May 8th, 1911. 

 The appearance of the mountain on the last of these 

 occasions is shown in Figure 91. The characteristic 

 features of these eruptions will be referred to later. 



After the eruption of 1783, the crater of the 

 Asama-yama was probably very deep and its diameter 

 less than at present. The first attempt to measure 

 its depth was made by Professor Milne in 1887. A 

 rope was stretched across the crater. On this a 

 pulley was run out with another rope that could be 

 lowered vertically, supplied with thermometers 

 at the end. When these had been lowered 

 seven hundred and thirty-five feet, thermometers 

 and rope were burnt, showing that the base of the 

 crater had been reached. In June, 1911, Professor 

 Omori made another attempt to sound the crater. 

 On this occasion, but little smoke issued from the 

 floor of the crater, and it was possible to see when it 

 was reached by the heavy weight lowered from a 

 part of the crater rim where the wall was vertical. 

 The depth was found to be about three hundred and 

 fifty feet, and this result was confirmed by measure- 

 ments made with a theodolite. Thus, in twenty-four 

 years, the floor of the crater has risen about three 

 hundred and eighty feet, so that, after the lapse of 

 another such period, if the rate of elevation should 

 continue uniform, the floor will be brought up level 

 with the margin of the crater. 



During the first two months of 1911, seismographic 

 observations were made at a temporary station at 

 Ashino-taira,on the south-west flank of the mountain, 

 at a height of six thousand three hundred feet above 

 sea-level. From January 9th to February 28th, 

 thirty-nine earthquakes were registered. All of 



