VOLCANOES 337 
Since many volcanoes are in the sea, or along its 
shores, a great percentage of the ash from the eruption 
falls upon the ocean; and being light enough to float 
in water, much of it drifts away to distant regions. 
So in an ash eruption, only a part of the ejected mate- 
rial gathers near the cone, but in the lava outburst. it 
all accumulates near the point of escape. 
Asa result of these differences, we find those cones 
that always erupt ash, very high, but relatively narrow 
at the base (Fig. 204). The cone is built-up to a 
Profile to show differences in area and steepness of ash (inner figure) and 
lava volcanoes (outer figure). 
considerable elevation by the constant accumulation 
of ash near the point of ejection, but much of it passes 
away in the air or water. In a cone erupting lava, 
on the other hand, the liquid rock tends to flow away, 
like any rather pasty liquid, all staying in the neigh- 
borhood of the crater. So the mass which accumulates 
in such a case, is greater than that in an ash-erupting 
voleano which has emitted the same amount of ma- 
terial; but its height is less, because the lava tends 
to flow away from the place of ejection. 
The lava flow may extend for a distance of twenty 
to forty miles, with a breadth of two or three miles, and 
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