Beagle Expedition (1831-1836); Geology -- South America; Volcanoes
A bare, undulating tract, at the eastern end of Chatham Island, is
remarkable from the number, proximity, and form of the small basaltic
craters with which it is studded. They consist, either of a mere
conical pile, or, but less commonly, of a circle, of black and red,
glossy scoriae, partially cemented together. They vary in diameter from
thirty to one hundred and fifty yards, and rise from about fifty to one
hundred feet above the level of the surrounding plain. From one small
eminence, I counted sixty of these craters, all of which were within a
third of a mile from each other, and many were much closer. I measured
the distance between two very small craters, and found that it was only
thirty yards from the summit-rim of one to the rim of the other. Small
streams of black, basaltic lava, containing olivine and much glassy
feldspar, have flowed from many, but not from all of these craters. The
surfaces of the more recent streams were exceedingly rugged, and were
crossed by great fissures; the older streams were only a little less
rugged; and they were all blended and mingled together in complete
confusion. The different growth, however, of the trees on the streams,
often plainly marked their different ages. Had it not been for this
latter character, the streams could in few cases have been
distinguished; and, consequently, this wide undulatory tract might have
(as probably many tracts have) been erroneously considered as formed by
one great deluge of lava, instead of by a multitude of small streams,
erupted from many small orifices.
Public-domain text, read in full here on John Shaqi.
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