EAST
RIVER: A TIDAL STRAIT IN NEW
YORK CITY
This
Earthcache is dedicated to Kenneth J. Kane, aka eastriver, who, on
June 28th 2000, placed the first canadian cache (GCBBA /
GC41) near East River (Nova Scotia)
Canada.
The body of water known under the
name of “East River” (or once also known under the name
of “Sound River”), is not an actual river at all. By
definition, a river flow from inland fresh water source, such as
mountain runoff or spring. Or, the East River is rather a narrow,
navigable channel of salted water, connected on both ends to the
Atlantic Ocean. It connects Upper New York Bay on its south end to
Long Island Sound on its north end and it separates Long Island
(including the boroughs of Queens and Brooklyn) from the island of
Manhattan and the Bronx on the North American mainland. Therefore,
by definition, it is a marine tidal strait. Because of tides, it
appears to flow like a river.
The East River is 16 miles (26 kilometers) long and from
600 to 4000 feet (183 to 1 219 meters) wide.
The physical environment of New York
City and its surroundings reflects the culmination of geologic
processes affecting the North American continent for more a billion
year period. Highlights of this geologic story include the
formation and the destruction of ancient mountain ranges and
seaways created by the shifting and colliding of ancient land
masses. This area is primarily composed of sediments that were
metamorphosed during the Taconic and Acadian orogenies around 500
to 400 million years ago. Garnets can be found in the rocks of
Hartland Formation and Manhattan Schist and it is in these hard
rocks that the city skyscrapers have their foundation. More
recently, in geological terms (Pleistocene epoch or “Ice
Age”: from 1.8 million years ago to 8 000 years ago),
there were episodes of continental glaciation when ice sheet spread
southward from eastern Canada into this area of USA. Around
17 000 years ago, the part of Wisconsin glacier covering the
New York City was about 985 feet (300 meters) thick. Much of the
modern landscape owes its character to the sculpting forces of
glacial ice and the erosion by rivers south of the ice front.
Between 17 000 years ago to 11 000 years ago, large ice
sheets bulldozed the landscape. Rocks with the glaciers scrapped
and scratched the bedrock of Central Park, producing long linear
striations and grooves. Long Island is composed of rubble (glacial
till or moraine) that glacier left behind as it melted. In this
period, around 11 000 years ago, the channel of East River was
formed by the retreating/melting of the glacier and advancing of
the Atlantic Ocean. According to one source, the difference in the
shape of the channel between its lover (southern) and its upper
(northern) portions is the best evidence of the glacial activity.
The upper portion (from Long Island Sound to Ward’s Island)
is wide, meandering, and has deep narrow bays on the both banks,
scoured out by the glacier’s movement. This portion runs
largely perpendicular to the glacial motion. The lover portion
(from Ward’s Island to New York Bay) is narrower, with
straight banks. This portion runs north-south, parallel to the
glacial motion. From the formation of the channel, it took at least
another 5 000 years, before the area found the aspect similar
to the one we know today.
Ever since its discovery by
Europeans, tides and strait’s naturally narrow channel, have
caused problems for generations of sailors. Especially the passage
located at its midpoint (along the east of Ward’s Island)
called the Hell Gate. It wasn’t until 1885, that its last
dangerous rocky reefs were cleared out by the largest (non atomic)
explosion caused intentionally by man. But the strait still posses
challenges. Its swift current, with water moving as fast as four
knots, can be dangerous to those who underestimate it.
The strait is joined in its northern
section by the Bronx River. North of Ward’s Island, it is
joined by the Bronx Kill. On the south side of Ward’s Island,
it is joined by another strait: the Harlem River. It is also via
Harlem River and Spuyten Duyvil Creek, that the strait connects
with the Hudson River. On Long Island,
Newtown Creek drains into the strait, forming part of the boundary
between Brooklyn and Queens. The strait contains several islands in
its upper and lower sections. It is spanned by eight bridges and
thirteen tunnels.
Historically, after the establishment
of Europeans in the area, the lower portion of the strait was one
of the busiest and most important channels in the world,
particularly during the first three centuries of the New York City
history. The first bridge to span the strait was the Brooklyn
Bridge. Opened in 1883, it had replaced frequent ferry
services.
Some useful
information…
- Sedimentary rock
is a type of rock formed by sedimentation of material either at the
surface or within the water bodies of Earth. The process causes
mineral and/or organic particles to settle and accumulate. These
rocks represent around 5% of the total volume of Earth’s
crust. Examples of rocks: limestone and sand stone.
- Metamorphic rock
is the result of transformation of an existing rock type, the
protolith, in process known as metamorphism (change in form). The
protolith (which may be sedimentary rock or another older
metamorphic rock) is subjected to heat (more than 150 to 200
degrees Celsius) and pressure (more than 1500 bars) causing
profound physical and/or chemical change. These rocks represent
around 95% of the total volume of Earth. Examples of rocks:
sillimanite, kyanite, garnet, feldspars and quartz.
- Orogeny (from
Greek: “oros” for mountain and “genesis”
for birth or origin) refers to forces and events leading to a
severe structural deformation of Earth’ crust due to the
engagement of tectonic plates. It is
the primary mechanism by which mountains are built on continents.
Taconic and Acadian are the names of two of these
orogenies.
- The geology of New
York City is pretty complicated. In few words, the rocks underlying
Manhattan, the Bronx, parts of Queens and Staten Island, constitute
the physiographic units of so called New England Upland. This
upland is divided by Cameron Thrust Fault in two parts. The rocks
occurring west of the fault are known as Manhattan Formation and to
the east are known as Hartland Formation.
- Wisconsin is the name given to the last glaciation
in North America.
The given coordinates will bring you somewhere on the banks
of the strait.
In order to register this
Earthcache:
Contact
the cache
owner
and meet those conditions
:
First, post a picture of you AND/OR
your GPSr standing at the coordinates with the strait in the
background. This photo has to be posted with your log, once
you’ll get the permission to log from us.
Second, in addition, e-mail us (do not post it in your
log!) the answers to the following questions:
1) Under which name is this section of
the strait known?
2) What is the elevation (altitude) at
the coordinates?
3) Facing the strait: What is the name
of the landmass you can see across this section of the
strait?
4) According to your judgement, what is
the distance from the coordinates to the other side of the
strait?
5) Looking at the outcropping rocks of
the strait’s banks: What is their color?
6) According to what you know: Are these
sedimentary or metamorphic rocks?
Sources of information:
Internet
Various leaflets and brochures found at the different
Visitor Centres of New York City and New York State.