Geology of Sandy
Hook
Sandy Hook is a barrier spit located in Middletown Township in
Monmouth County, NJ, that is between 6 and 7 miles in length and
varying between 0.10 and 1 miles in width. Barrier spits are
somewhat linear landforms that extend away from the mainland into a
body of water and are typically composed of sand, silt, or small
pebbles. Geologically, Sandy Hook is an extension of a barrier
peninsula along the coast of New Jersey, and is separated from the
mainland by the estuary of the Shrewsbury River. On its western
side, the peninsula encloses Sandy Hook Bay, a triangular arm of
Raritan Bay and the southern entrance of Lower New York Bay south
of New York City. Early Dutch settlers called the area "Sant Hoek;"
with the English "Hook" deriving from the Dutch "Hoek," meaning
"spit of land".
Spits typically form where the direction of the shore inland
re-enters, or changes direction, greater than 30 degrees and
continue out into the sea until water pressure (such as from a
river) becomes too much to allow for sand deposition. Sandy Hook
has formed where currents from the Atlantic Ocean and Lower Raritan
Bay meet the Raritan River to promote deposition of granular
materials, resulting in localized shallowing, or shoaling, of the
water that stretches over four miles into the Atlantic Ocean. The
sediments that make up spits come from a variety of sources
including rivers and eroding bluffs, and changes there can have a
large impact on spits and other coastal landforms.
At this location, the current spreads out or dissipates,
dropping much of the sediment that the water has been carrying.
Sediments build underwater, eventually forming a submerged bar.
Littoral drift continues to transport sediments in the direction
the waves are breaking, eventually forming an above-water spit.
Littoral drift occurs due to waves meeting the beach at an oblique
angle, and backwashing perpendicular to the shore, moving sediment
down the beach in a zigzag pattern. The drifting is complemented by
currents, which transport sediment through the water alongside the
beach. These currents are set in motion by the same oblique angle
of entering waves that causes littoral drift and transport sediment
in a similar process. Without the complementary process of littoral
drift, the bar would not build above the surface of the waves and
would instead be leveled off underwater. Towards the end of a spit
where the water opens up, wave refraction can also occur, carrying
sediment around the end to form a hook, or recurved spit.
Year by year, littoral currents in conflict with strong tidal
currents deposit large quantities of sand in this area, causing the
size and shape of Sandy Hook to continually evolve and posing a
serious navigational hazard for vessels seeking to bring goods to
and from the ports around New York City.
The Sandy Hook Light - Gateway to New
York
Records show that a lighthouse at
the tip of Sandy Hook to help guide ships safely into the main
shipping channel had been suggested as early as 1679. However, it
wasn't until several shipwrecks occurred in the first three months
of 1761 that decisive action was taken. On March 13, 1761,
forty-three prominent New York merchants successfully petitioned
Caldweller Colden, President of His Majesty’s Council of New
York, for a lighthouse to mark the entrance to New York Harbor.
Originally called the New York Lighthouse, the tower on Sandy
Hook was built of rubblestone under the guidance of Isaac Conro, a
mason and builder from New York City. The beacon was first lit on
June 11, 1764. As the lighthouse's primary purpose was to guide
vessels into New York Harbor, the clerk of the Master and Wardens
of the Port of New York, was authorized to collect three pence a
ton from ships entering the harbor to pay the annual salary of the
lighthouse keeper. In its bicentennial year, Sandy Hook Light was
designated a National Historic Landmark, and a commemorative plaque
was mounted on the tower as part of a celebration held at the site.
Ownership of the lighthouse was transferred to the National Park
Service in 1996.
Sandy Hook has also served as a military defense post for the
waterways leading to New York City. The now-defunct Fort Hancock is
located at the north end of the peninsula and is now open to the
public. The Sandy Hook Proving Ground was used by the United States
Army for many years – beginning after the Civil War until
1919, when the facility was moved to Aberdeen, Maryland – and
was later the site of a Nike missile defense installation. The
Sandy Hook Nike station is one of a very few stations that are
still intact. Almost all of the fort's gun batteries are off limits
to the public due to their hazardous condition. The exception to
this is Battery Gunnison which is being restored by volunteers and
also has two M-1900 six-inch cannon installed; the weapons were
placed there in 1976. Guided tours give visitors a look at an
actual Nike missile, the missile firing platforms, and a radar
station (complete with 1960's-era computers).
To obtain credit for this Earthcache, there are three
activities that must be performed:
1) You must visit the Sandy Hook Light. Post a picture of
either you or your GPS at the historic plaque at the base of the
lighthouse tower. Other pictures of the lighthouse are welcome
additions to the gallery, but not necessary.
2) Behind the tower is a building housing a small theater
with an informational video about the lighthouse and the history of
Sandy Hook. There is no fee to watch the film and it is available
at all times, even when the lighthouse visitor center is closed.
Start the video by pressing one of the buttons on the wall under
the television. After watching the video, send an email to the CO
with the answers to the following questions:
a. How far was the Sandy Hook Light originally from the tip of the
point?
b. How far is the Sandy Hook Light from the tip of the point
today?
c. What geological forces have caused the apparent motion of the
lighthouse from the shoreline?
(Note: If the movie is unavailable, most all of the answers
can be found on information signs around the area. Cache can still
be logged if the movie is not playing.)
3) Visit one of the historic military sites located within
the Fort Hancock section of Sandy Hook. Post your picture of you
and your GPS at the location you choose to visit. In the same email
as question 2, explain how the underwater geology and geography of
the area made Sandy Hook of such strategic military importance for
defense of the harbor. (Hint: It is also the reason that a
lighthouse was considered a necessity at this location as explained
in the lighthouse video).