Jökull - 01.01.2001, Page 53

Caldera formation at Cerro las Cumbres, Mexico
Figure 3. Graphic logs showing the stratigraphy of the las Cumbres deposits at selected sections. Section loca-
tions are shown in Figures 2a and 2b. – Valin snið í gegnum gosefnin frá eldgosinu sem myndaði öskjuna á Las
Cumbres. Staðsetning sniðanna er sýnd á myndum 2a og 2b.
lain by T–II dacitic plinian tephra from Pico de Oriz-
aba (Höskuldsson and Robin, 1993). In distal areas
on the eastern slopes of Pico de Orizaba a tephra
layer less than 1 cm thick was observed in soil pro-
files. The Cerro Las Cumbres tephra is distinguished
from those originating at Pico de Orizaba by their dis-
tinguishing phenocrysts. Stratigraphically the Cerro
Las Cumbres tephra layer is situated between the T–I
and T–II tephra layers derived from Pico De Orizaba
(Höskuldsson and Robin, 1993). Reworked pumice
rich in biotite was observed on alluvial plains close to
the town of Tierra Blanca, about 150 km east of the
volcano. No primary pyroclastic–flow deposits were
observed to the east of the volcano, indicating that the
distribution of the pyroclastic–flow deposits was lim-
ited to the western slopes.
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