"Stark's Knob is a mass of volcanic rock of unknown age
and relations, locally known as a volcano, which probably holds the
key to the interpretation of some of the geological history of this area and
western New England..."
From a report of the
State Geologist, New York State Museum, in 1952.
Stark's Knob is formed of volcanic rock, but is not an old volcano. The triangular "volcano shape" shape
of the hill is due to early quarrying that removed the east side
of the hill. The significance of the
hill is that it is a submarine pillow lava
called pillow basalt - one of the very few in
eastern North America.
Volcanic rock is of two main types-1) Mount St. Helen's- or east
Pacific-type andesites, which result from explosive eruptions of
stiff, silica-rich lava (i.e., liquid rock), and 2) the Hawaiian
Island- or Icelandic-type that feature flows of very hot basalt
lava from deep in the earth.
"Pillows" form when basalt lava flows up from deep cracks (vents)
in the earth and erupts under water. A low ridge builds along an
elongated vent, and the basalt lava spills away from the vent.
The cooling basalt lava rolls downslope, and ball-like forms known
as pillows pile up.
The pillows in pillow basalt have convex upper surfaces. When a
pillow rolls onto and settles on older pillows, its lower surface
shows concave depressions that conform to the rounded tops of
underlying pillows. If you inspect Stark's Knob pillows closely,
you can determine that this pillow basalt deposit has been tilted
sharply to the west because the convex pillow tops are inclined
west (away from the Hudson River). Small cavities, sometimes filled
with the mineral calcite, are ancient steam bubbles within the pillows.
Stark's Knob and Taconic Mountain-Building
Pillow basalts from western Newfoundland in Canada, to
Stark's Knob in New York; and south into New Jersey and
Pennsylvania are similar in age and reflect the first orogeny
(mountain-building episode) in the Appalachians. This is the
ca. 460 to 440 million year old Taconic orogeny.
The Taconic orogeny featured a collision of the eastern edge of
ancient North America with a volcanic island arc similar to
modern-day Japan. Remnants of this explosive volcanic island arc
are preserved along the modern Connecticut River valley.
As the volcanic arc was pushed west into Vermont and eastern New
York and the continent buckled in front of it, cracks opened in
the earth's crust. The Stark's Knob basalt lava flowed out of
these cracks into the sea covering eastern North America. Fossil
snails found between the basalt pillows by State Museum researchers
indicate an Early or, more likely, Middle Ordovician age of the
pillow basalt. These snails also show that the pillows were formed
in relatively shallow sea water.
With continued thrusting of the island arc, the Stark's Knob
pillow basalt was caught under the Taconic thrusts and up ended,
so that it is no longer flat lying.
The site is important as many classes of geology students and
professional geologists from far and near visit the site. It provides a rare opportunity to
study this phenomenon, in part due to the cross-cutting rock exposure created when mining activities were
concentrated here at the turn of the last century.
The reason most people refer to this feature as a "volcano"
probably comes from early accounts, beginning in the early 20th century:
It has been described at length in the reports of the Geological Survey as a volcano or volcanic plug and as such is the
only geological phenomenon of this kind known to occur in the State
of New York.
(from the Report of the Director
of the New York State Museum, 1913)
The fact that this hill is not evidence of a once thundering volcano standing beside the Hudson River
does not detract at all from its monumental geological interest and
For more information...
If you have questions, or wish to obtain more detailed information about this subject,
New York State Museum
Room 3107 Cultural Education Center
Albany, New York 12230