La Reforma
La Reforma has usually been considered to be a fine example of a caldera
containing what is called a "resurgent dome." A circular depression (like a
moat) surrounds a central high area of uplifted sedimentary rocks. The moat
has been interpreted to be a caldera wall, and the uplifted rocks the
resurgent dome--intrusive rocks that bowed the caldera floor upward after
caldera collapse. An alternative interpretation is that the updoming
occurred first, and that the extensive ash deposits erupted from around its
base. In this second scenario the moat is not the old caldera wall, but
instead an erosional feature developed around the base of the dome. La
Reforma is indeed an interesting structure, and deserves further study.
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