Geography Reference
In-Depth Information
72
Figure 3.4. Ice fumaroles
stand as sentries near the
summit of Mount Erebus.
Formed by the freezing
of vapors emitted by the
volcano, the taller struc-
tures are about ten feet in
height. Kenyite lava crops
out on the right.
was pumice, a frothy, brown glass that crumbled with the force of their thumbs, chock
full of the finest faceted crystals of a rare type of feldspar called anorthoclase. The lavas
around Cape Royds also were full of anorthoclase crystals, but there they were not much
more than an inch in length and stuck solidly in the rock. Here the crystals ranged up
to three inches, some having the classic rhombic shape, others with intricate twins pro-
truding as symmetrical adornments on the primary crystals. Because the pumice was so
crumbly, the anorthoclase weathered out of the glass, and was so concentrated at places
that it almost formed scree. Most of the crystals were coated with a pale yellow crust of
sulfur that added a burnish to their otherwise gray coloration.
Professor David was the one who had first identified the anorthoclase back at the win-
ter quarters. He explained that they were characteristic of a volcanic rock called kenyite,
named for its best known occurrence, in East Africa at Mount Kilimanjaro and Mount
Kenya. What Mount Erebus shares with its East African kin is location—not geographical
location, for they are at the extremes of latitude, but rather geological location, with each
being found in the interior of a continent. More typically, volcanoes form in arcs at conti-
nental margins or in ocean basins, where one would never find kenyite. Everyone picked
up a pocketful of the crystals before heading back to camp. They would make wondrous
gifts for the grandchildren, when the old men told their tales of fire and ice.
The day was mercifully calm after the previous day's storm. The men easily lit the
