America's Volcanic Past -
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| "Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994 |
Volcanic Highlights and Features:
[This list is just a sample of
various New Jersey volcanic features or events and is by no means inclusive.]
New Jersey’s landscape has formed during more than a billion years of geologic processes such as mountain building, erosion and deposition. This history has given the State distinctive landforms that are divided into four regions, known as physiographic provinces. Beginning in the northwest and proceeding southeast, these regions are called the Valley and Ridge, Highlands, Piedmont, and Coastal Plain Provinces. The first three are grouped with the larger classification known as the Appalachian Highland, the last with the Atlantic Slope. Both are major physiographic divisions of the United States.
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The Appalachian Highland:3
The Atlantic Slope:3 The Atlantic Plain (Atlantic Slope) is the flattest of the provinces. It stretches over 2,200 miles in length from Cape Cod to the Mexican border and southward another 1000 miles to the Yucatan Peninsula. The Atlantic plain slopes gently seaward from the inland highlands in a series of terraces. This gentle slope continues far into the Atlantic and Gulf of Mexico, forming the continental shelf. This region was born during the breakup of the supercontinent Pangea in the early Mesozoic Era.
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New Jersey's Valley and Ridge Province:1,2
New Jersey's Highlands Province:1,2
New Jersey's Piedmont Province:1,2
Rocks of the Piedmont Province are separated from the
rocks of the Highlands Province by a series of major
faults, including the Ramapo Fault. The more
resistant gneisses and granites on the upthrown
northwest side of the faults make a prominent
escarpment, 200 to 800 feet in height, extending from
Mahwah through Boonton and Morristown to Gladstone,
and from there westward in an irregular line to the
Delaware River near Milford. South and east of this
escarpment, interbedded sandstone, shale,
conglomerate, basalt, and diabase of the Piedmont
Province underlie a broad lowland interrupted by
long, generally northeast-southwest trending ridges
and uplands. The rocks of the Piedmont are of Late
Triassic and Early Jurassic age (230 to 190 million
years old). They rest on a large, elongate crustal
block that dropped downward in the initial stages of
the opening of the Atlantic Ocean -- one of a series
of such blocks in eastern North America. These
down-dropped blocks form valleys known as rift
basins.
Volcanic activity was also associated
with the rifting, as indicated by the basalt and
diabase interlayered with the sandstone and shale.
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone. The basalt and diabase are extensively
quarried for crushed stone.
New Jersey's Coastal Plain Province:1
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| New Jersey Counties with Volcanic Rocks |
Bergen County:2
Outcrops of Jurassic basalt, western edge of Bergen County ...
Outcrops of Jurassic diabase, eastern edge of Bergen County ...
Outcrops of Precambrian gneiss or granite, northern tip of Bergen County
Essex County:2
Outcrops of Jurassic basalt, western Essex County
Hudson County:2
Outcrops of Jurassic diabase, central and eastern Hudson County
Hunterdon County:2
Small areas of outcropping of Jurassic basalt, northeast corner of
Hunterdon County, and central Hunterdon County ...
Outcrops of Jurassic diabase, southern Hunterdon County and north central
Hunterdon County ...
Outcrops of Precambrian gneiss or granite, northern Hunterdon County
Mercer County:2
Outcrops of Jurassic diabase, northern edge of Mercer County ...
Small area of Precambrian gneiss or granite, central Mercer County
Middlesex County:2
Outcrops of Jurassic diabase, west central Middlesex County
Morris County:2
Outcrops of Jurassic basalt, small sections of
northeastern and southeastern Morris County ...
Outcrops of Precambrian gneiss or granite, western half of Morris County
Passaic County:2
Outcrops of Jurassic basalt, southeastern Passaic County ...
Outcrops of Precambrian gneiss or granite, western half of Passaic County
Somerset County:2
Outcrops of Jurassic basalt, northeast Somerset County ...
Outcrops of Jurassic diabase, southern tip of Somerset County ...
Outcrops of Precambrian gneiss or granite, northern tip of Somerset County
Sussex County:2
Outcrops of Precambrian gneiss or granite, eastern and southeastern Sussex
County
Union County:2
Outcrops of Jurassic basalt, northwestern tip of Union County
Warren County:2
Outcrops of Precambrian gneiss or granite,
southeastern Warren County
| Byron Diabase |
Byron Diabase:4
Exposures of a diabase sill crop out along Route 29 at Byron, New Jersey. The diabase is highly fractured, with joints filled with minerals including amphibole, calcite, epidote, and prehnite. The diabase intruded into the Lockatong Formation probably during the Early Jurassic when all the other volcanism occurred in the region.
| Cushetunk Mountain |
Cushetunk Mountain:2
Diabase
is a rock formed by the cooling of magma at
some depth in the crust;
basalt
is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
| Hook Mountain |
Hook Mountain:2
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
Hook Mountain Basalt:4
The Hook Mountain Basalt stands out as the upper high wall of the quarry near the top of the hill. A thin, light-colored chill zone represents the effect of contact metamorphism in the sedimentary rock along the base of the lava flow. The basalt displays an abundance of vesicles, small vertical holes formed from gases venting from the lava before it cooled. The basalt in the quarry wall also displays poorly-developed columnar jointing. Some of these vesicles and fractures yield the pale green zeolite mineral, prehnite.
| Long Hill |
Long Hill:2
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
| Newark Basin |
Newark Basin:4
The Newark Basin (in New Jersey, New York, and Pennsylvania) and the Connecticut River Basin are both "aborted rift" basins (rift basins that are no longer actively widening via rift-style tectonism and are no longer collecting sediments). Sediments began to accumulate in both basins during the Late Triassic.
Both basins are half grabens which contain characteristic sedimentary conglomerates, sandstones, and mudrocks that usually bear a red or brownish appearance from an abundance of iron oxide minerals.
...
Both the Newark and Connecticut River Basins contain "traprocks." The word, traprock, is derived from the Swedish word "trappa," meaning stair or step. In the mining usage, a traprock is any fine-grained igneous rock, ususally diabase or basalt, that can be crushed for building or road aggregate. Erosion creates their step-like appearance, producing abrupt termination of successive volcanic flows. During early Jurassic time, episodic rift-basin-style volcanism began to occur. Magma of basaltic composition migrated from the upper mantle to the surface along faults. Massive volcanic eruptions at the surface resulted in the formation of surface flows that spread for great distances across the low relief of the alluvial basins. After volcanism ended, the flows were buried beneath the more gradual accumulation of basin sediments. Because of the half-graben structure of these basin, the originally horizontal volcanic flows are now gently inclined. The resistance of traprocks to erosion (relative to the surrounding sandstone and shale) results in the formation gently dipping cuestas throughout the Mesozoic basins all along the Atlantic margin. Within the Newark Basin, the Watchung Mountains are examples of traprock questas. The ridges of resistant volcanic rock of the Palisades and the Watchung Mountains display steep escarpments on their eastern flanks and gentle slopes on their western flanks. This is an indication of the gentle dipping character of the strata towards the deeper western side of the basin. When the sediments were originally deposited there were probably nearly flat-lying. The structural dip of the rock probably developed as the basin continued to grow through time, even long after the youngest sediments of the basin were deposited.
| Orange Mountain Basalt |
Orange Mountain Basalt:4
Pillow lavas can be seen in the abandoned traprock quarries throughout the hillsides in the Paterson area. Minerals occur in fractures and in gas pockets that formed within the pillows of lava as they cooled. Some of the hollow chambers in the rock were probably lava tubes that drained before the lava cooled. The quarries in the Orange Mountain Basalt utilized the traprock primarily for construction material. Unfortunately, these quarries are closed to public access, but they are frequently the target of organized societal and college field trips. Mineral collecting within these quarries can be quite hazardous due to falling debris from the high walls, especially during the freeze-thaw cycles in the winter. Don't attempt to collect minerals without permission. If interested, be patient, and join a local mineral club or society on a trip.
Along Interstate 280:4
Driving westward along Interstate 280 the highway crosses the valley west of Newark ... the highway begins to ascend the grade rising to the ridge top of the 1st Watchung (Orange Mountain) ...
The cliffs consist of a single massive lava flow that cooled and cracked into columnar joints. The unusual feature of this flow are the complexity of the columnar joints. In some locations, the joints tend to radiate away from a central core. These patterns were generated by an uneven cooling pattern in the flow, possibly a result of degassing structures or uneven mixing of the lava as it cooled.
| Patterson Falls |
Patterson Falls:4
The falls spill over a resistant ridge into a chasm carved in the lower flow of the Orange Mountain Basalt where it overlies the upper contact of the Passaic Formation. In the vicinity of the falls, glacial erosion has stripped away the upper more friable pillow lavas. These pillow lavas can be seen in the abandoned traprock quarries throughout the hillsides in the Paterson area. Minerals occur in fractures and in gas pockets that formed within the pillows of lava as they cooled. Some of the hollow chambers in the rock were probably lava tubes that drained before the lava cooled. The quarries in the Orange Mountain Basalt utilized the traprock primarily for construction material. Unfortunately, these quarries are closed to public access, but they are frequently the target of organized societal and college field trips. Mineral collecting within these quarries can be quite hazardous due to falling debris from the high walls, especially during the freeze-thaw cycles in the winter. Don't attempt to collect minerals without permission. If interested, be patient, and join a local mineral club or society on a trip.
| Riker Hill Park |
Riker Hill Park:4
Riker Hill Park is an excellent location to examine fresh exposures of sedimentary red beds and basalt typical of the Newark Basin region. The park is located along the western side of the Newark Basin near Rosedale, New Jersey, close to the intersection of Interstate 280 with Interstate 287.
Hook Mountain Basalt:4
The Hook Mountain Basalt stands out as the upper high wall of the quarry near the top of the hill. A thin, light-colored chill zone represents the effect of contact metamorphism in the sedimentary rock along the base of the lava flow. The basalt displays an abundance of vesicles, small vertical holes formed from gases venting from the lava before it cooled. The basalt in the quarry wall also displays poorly-developed columnar jointing. Some of these vesicles and fractures yield the pale green zeolite mineral, prehnite.
| Rocky Hill |
Rocky Hill:2
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
| Sourland Mountains |
Sourland Mountains:2
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
| The Palisades |
The Palisades:4
The Palisades were designated a "National Natural Landmark" being "the best example of a thick diabase sill in the United States." The sill extends southward beyond the cliffs in Jersey City beneath the Inner Harbor, and reappear on Staten Island. The Palisades are the eroded cross-section of a large intrusive diabase sill that intruded between layers of sandstone and shale of the Late Triassic Stockton and Lockatong Formations. (In the Staten Island area, the strata equivalent to the Lockatong Formation is called the Brunswick Formation.) The sill approaches 1,000 feet thick and was probably fed from an unknown stock buried beneath the basin to the west. Radiometric age determinations of the diabase suggest that the sill formed in multiple stages between about 192 to 186 million years ago (late Early Jurassic).
Olivine Layer:4
Within the lower portion of the sill there is a zone of rock enriched in olivine, a high temperature ultramafic mineral that formed first and settled to the bottom of the intrusion before the rest of the magma cooled. This zone is about 10 to 15 feet thick, and crops out along and above the road in the Ross Dock area near the south entrance to the park.
The Palisades Diabase:2
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
The Palisades and the Lincoln Tunnel:4
An outcrop of diabase at the top of the cliffs is one of the first thing you see when you emerge onto the ramp from the Lincoln Tunnel on the New Jersey end.
| Wachung Mountains |
Wachung Mountains:2
Diabase is a rock formed by the cooling of magma at
some depth in the crust; basalt is formed by cooling
of an identical magma that has been extruded onto the
surface as lava. Both basalt and diabase are more
resistant to erosion than the enclosing sandstone and
shale and therefore they form ridges and uplands.
The Palisades, Rocky Hill, Sourland Mountains, and
Cushetunk Mountain are underlain by diabase layers.
The Watchung Mountains, Long Hill, and Hook Mountain
are underlain by basalt layers. Valleys and lowland
between these ridges are underlain by shale and
sandstone.
Along Interstate 280:4
Driving westward along Interstate 280 the highway crosses the valley west of Newark ... the highway begins to ascend the grade rising to the ridge top of the 1st Watchung (Orange Mountain) ...
The cliffs consist of a single massive lava flow that cooled and cracked into columnar joints. The unusual feature of this flow are the complexity of the columnar joints. In some locations, the joints tend to radiate away from a central core. These patterns were generated by an uneven cooling pattern in the flow, possibly a result of degassing structures or uneven mixing of the lava as it cooled.
Wachung Reservation:4
The Watchung Reservation is a nature preserve encompasses 2,000 acres straddling portions of the 1st and 2nd Watchung Mountains to the south and west of the Milburn near Scotch Plains, New Jersey. There are a variety of locations in the area worth examining, including exposures of Early Jurassic red beds and basalt flows.
Excerpts from:
1) New Jersey Geological Survey Website, 2004
2) Geologic Map of New Jersey, 1999: New Jersey Geological
Survey, Department of Environmental Protection,
Division of Science, Research and Technology
3) USGS/NPS Geology in the Parks Website, 2001
4) Stoffer, Phil, 2003, Geology of the New York City Region, A Preliminary Regional Field-Trip Guidebook:
U.S. Geological Survey Website, 2004.
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