Vibe-Fall-2024 - Flipbook - Page 62
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VOLCANOES
THE VOLCANIC LEGACY OF THE OSSIPEE MOUNTAINS
By Matt Maloney, Tin Mountain Conservation Center
The Ossipee Mountains are one of the world’s premier examples of a ring dike that is preserved
within a mountain range. The Moat volcanic rocks found in the Ossipees, Moats, and elsewhere in the
White Mountain and Lakes regions tell a remarkable story that geologists are still unravelling.
O
ne of the most unique and remarkable geographic features in all of
the Eastern United States is the
circular-shaped mountain ridge known
as the Ossipee Mountains. A mountain
range shaped like a donut conjures up a
whole range of questions as to its origins
and serves as a wonderful example of the
problem-solving involved in interpreting
the shape and form of our local landscape.
These mountains tell of an era when an
ancient supercontinent’s time was ending
and the first inklings of a basin that became
the Atlantic Ocean started to submerge.
A key to understanding the curious
donut shape of the Ossipees is the
concept of a volcanic ring dike.
Indeed, the Ossipee Mountains
are one of the world’s premier
examples of a ring dike that
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is preserved within a mountain range. The
narrow ring-shaped bedrock dike that
wraps around the slopes of the Ossipees is
made of a rock that is the remnants of magma that seeped up through a collapsed volcanic caldera. The magma crystallized into
a rock known as syenite, rich in the mineral
feldspar. Preserved within the remnants of
this volcanic caldera are deposits of ash and
lava flows that once covered much of New
Hampshire and are now known as the Moat
volcanic rock. Much of the Moat volcanic
rock comprises the ridgelines and summits
of the Ossipee Mountains.
These Moat volcanic rocks are found
sparsely in only a few locations, all within
the White Mountain and Lakes regions
of New Hampshire. The namesake of this
volcanic rock is Moat Mountain in North
Conway, which is also a range containing
many large areas of the remnants of
ancient volcanoes’ pyroclastics. The Moat
volcanic rock has frozen in time those
ancient outpourings of lava and ash. Moat
Mountain has the thickest known deposits
of these rocks.
The Moat volcanic rocks found in the
Ossipees, Moats, and elsewhere in the
White Mountain and Lakes regions tell a
remarkable story that geologists are still
unraveling. As a resident of or visitor to
the Lakes and White Mountain regions
with a casual interest in geology, there is
a fascinating history to be discovered in
these rocks. This bedrock that composes
our mountains serves as a beacon from
the deep past, a time that extends before
there were mammals and well before
humans came along.
Contrary to what many hear, or
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