p. Waits — Popocatepetl Again in Activity. 87 



bowlders slowly accumulating in the crater, may be so 

 far increased that it will be able to throw the contents 

 of the crater into the air by a single formidable eruption. 

 In this case we have to expect and to fear the occurrence 

 of glowing clouds (Glutwolken, nuees ardentes). We 

 have had an opportunity to observe and to study this 

 phenomenon also on the volcano of Colima. There in 

 1913 the contents filling the entire crater up to the rim, 

 as well as the mass filling the chimney to a great depth, 

 and even the upper 150 m. of the crater cone, were thrown 

 into the air by one single eruption and blown into dust 

 partly by the explosion itself, partly by the fall of the 

 masses on the cone and into the crater. Glowing clouds 

 rolled down the flanks of the cone for several days and 

 accumulated in the barrancas at the foot, where they 

 flowed to a distance of about 12 km. from the crater. 



Fortunately the Mexican volcanoes are not inhabited 

 (mthin a radius of 10 km. around the summit of Popo- 

 catepetl we do not find a single inhabited place and towns 

 do not exist within a radius of 15 km. ) ; and the country 

 furrowed by deep barrancas around the volcano would 

 place strong obstacles in the way of lava streams and 

 glowing clouds ; therefore even a very highly increased 

 activity of Popocatepetl would not have to be feared. 

 Greater damage could be caused by extraordinarily strong- 

 eruptions of ashes, as the flat roofs used in this part of the 

 country would not resist the weight of heavy masses of 

 ashes. 



Mexico, November, 1920. 



