Earthquakes and Volcanoes 



distance of more than fifteen miles from the 

 mountain. 



During an eruption, ashes are commonly 

 ejected in great quantity, but it must be borne 

 in mind that the materials so-called are very 

 different from the partially burnt fuel of the 

 domestic hearth. Volcanic ashes are, in fact, 

 nothing but fragments of lava, or partially-fused 

 rocky matter. When jets of this lava are shot 

 forth from the volcano, the liquid is broken up by 

 the air, and so splashed about that it falls in 

 drops, which harden into small spongy fragments, 

 resembling ashes and cinders. In some cases, 

 the lava is broken into such fine particles that it 

 is known as volcanic dust or sand ; dense showers 

 of such dust have been known to darken the sky 

 for miles around the volcano, and have been 

 wafted by winds for even hundreds of miles. 

 It is an interesting fact, shown by the examina- 

 tion of the sea-bottom by the Challenger, that 

 volcanic particles are almost universally distribu- 

 ted over the floor of the deep sea. 



When the steam, which is abundant in most 

 eruptions condenses in torrents of rain, the 

 volcanic dust is frequently worked up into a hot 

 mud which rolls down the hill in a sluggish 

 stream, burying everything before it. Hercu- 

 laneum was sealed up by a crust of volcanic mud 

 discharged from Vesuvius; while Pompeii was 

 overwhelmed by a vast accumulation of dust 

 and ashes during the same eruption. 



The partially molten rock called lava rises up 

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