The Geology of Edison, New Jersey

Overview of the Geologic History and Formation of Edison

Edison, New Jersey is located in the Piedmont physiographic province, between the Appalachian Mountains and the Atlantic coastal plain. The town lies atop ancient metamorphic and igneous bedrock, formed over 1 billion years ago during the Precambrian Era.

During the various ice ages over the last 2.6 million years, including the last glacial maximum around 21,000 years ago, sheets of ice advanced and retreated across New Jersey multiple times. These glaciations left significant impacts on Edison’s landscape, eroding bedrock, depositing glacial sediment, and helping shape the Raritan River valley that borders the town.

Key Geologic Time Periods for Edison’s Formation

Some of the key time periods that influenced the geology underlying Edison include:

Precambrian Era (>542 million years ago)

• Ancient igneous and metamorphic rocks like granite, gneiss, and schist formed as tectonic plates collided. These make up Edison’s basement bedrock today.

Various Ice Ages (2.6 million years ago to present)

• Advancing and retreating glaciers eroded bedrock, deposited sediment, and carved major river valleys.

Triassic Period (251-200 million years ago)

• Faulting associated with the breakup of Pangea formed Edison’s bordering Raritan River basin.

Cretaceous Period (145-66 million years ago)

• The Atlantic Ocean continued to open, stretching the earth’s crust underneath Edison.

Bedrock Geology Underlying Edison

Edison is situated atop ancient Precambrian igneous and metamorphic rocks over 1 billion years old. Drill samples taken across the town indicate this basement rock layer lies around 2,000 feet under the surface and consists primarily of granite, gneiss, schist, and quartzite.

Major Basement Rock Units

Key basement rock types underlying Edison include:

Granite

• Coarse-grained intrusive igneous rock with quartz, feldspar, mica, and other minerals

Gneiss

• Foliated metamorphic rock with light and dark banding

Schist

• Medium to coarse metamorphic rock with layered structure

Quartzite

• Metamorphosed sandstone rich in quartz grains

These ancient Precambrian formations were later involved in the assembly and breakup of the supercontinents Rodinia and Pangea, undergoing deformation, faulting, uplift and erosion which exposed them at the surface today across New Jersey’s Piedmont.

Structural Deformation Features

In addition to fossils and mineral composition, the structure of these metamorphic and igneous basement rocks provide clues to Edison’s past geologic history. Key structural deformation features include:

Foliation

• Planar alignment of minerals showing past tectonic strain

Faults

• Fractures where rock movement has occurred

Veins

• Mineral deposits filling cracks where fluid has circulated

Shear Zones

• Areas with extreme irregular strained rock fabric

By analyzing the orientation, density, and relative ages of these deformation features, geologists reconstruct past deformation events affecting the bedrock under Edison.

Surficial Geology and Glacial Features

Above the Precambrian basement rock underlying Edison lies up to 200 feet of relatively younger unconsolidated glacial sediments, fluvial deposits, and fill material that make up the surface geology across town. These layers provide a rich record of past glaciation and climate change.

Glacial Sediments

Most extensive across Edison are assorted glacial sediments deposited from advancing and retreating ice sheets during the Pleistocene Ice Age:

Terminal Moraines

• Irregular ridges of till and sediment marking pauses in past glacier margins

Outwash Plains

• Wide sandy zones of stratified glaciofluvial gravel and sand

Kames

• Short steep ridges composed of stratified glacial sediments

Kettles

• Steep depressions where buried glacial ice later melted

Together these features create an undulating, hummocky landscape pocked by depressions, ponds, and knolls built from sediment eroded far to the north. Variations in soil composition directly impact ecology and land use across town.

Post-glacial Deposits and Fill

In places glacial sediments have been covered by more recent stream, swamp, tidal, and human-introduced fill deposits:

Alluvium

• Clay, silt, sand, gravel deposited by flowing water

Peat

• Organic swamp muck containing woody debris

Estuarine Deposits

• Tidal silts and clays with organic material

Urban Landfill

• Mixed construction debris and other human refuse

Bog iron deposits also occur locally, representing former natural iron formations altered by groundwater. By studying soil boring samples, geologists map the distribution and thickness of these various surface sediment layers.

Modern Geological Features and Hazards

In addition to clues from Edison’s distant past, present-day geological features and processes shaping the landscape provide further insight into the town’s geologic history and environmental hazards residents may face.

The Raritan River Basin

Edison lies on the edge of New Jersey’s coastal plain, bounded to the east by the Raritan River basin which stretches from the Appalachian piedmont to Raritan Bay. This major river system helps drain water and transport sediment eroded from the town’s actively weathering bedrock and sediments.

Key features of Edison’s placement within the Raritan Basin include:

River Terraces

• Former buried floodplain levels marking old river courses

Ox-bow Lakes

• Curved swampy depressions representing abandoned meanders

Floodplains

• Low muddy plains adjacent to present river channels

Levees and Point Bars

• Raised ridges and banks built up along insides of river bends

This fluvial terrain contains a record of past migration in the Raritan’s channel alignment responding to changing water flow, sediment load, and sea level.

Seismicity and Earthquake Risks

While not directly on a tectonic plate boundary, seismic activity does present a potential hazard in Edison’s location amidst complex faulting zones related to the breakup of Pangea:

Small Local Faults

• Minor fractures in bedrock from relief of past stresses

Intraplate Seismic Zones

• Ancient zones of crustal weakness far from plate edges

Historic earthquakes with potentially significant shaking in Edison include:

• 1783 New York City quake (est. M4-5)
• 1737 New York / New Jersey quake (est. M5+)

While risks are lower compared to interplate regions, the seismic hazard in Edison still warrants earthquake resistant building design.

Additional Geologic Hazards

Beyond earthquakes, Edison faces a number of other significant geologic hazards:

Soil Liquefaction

• Loose wet sediments losing strength during shaking

Flash Flooding

• Rapid inundation of low-lying areas

River Flooding

• Overbank discharge from Raritan tributaries

Sinkholes/Subsidence

• Sudden collapse into open cavities

Understanding the town’s geology allows predicting, preparing for, and mitigating these hazards through proper land use policies, infrastructure design, emergency response, and public awareness.

Local Economic Impacts of Geology in Edison

Edison’s geologic history and resources have strongly influenced past and present economic development:

Iron Ore Mining

• Former mining of bog iron deposits in mid-1800s

Brick Making Industry

• Abundant glacial clays used historically for brickworks

Sand/Gravel Pits

• Outwash sediments a source of aggregate

Landfill Sitting

• Low swampy terrain utilized for waste disposal

In these ways the town’s geology has directly created jobs, shaped land usage patterns, and impacted the local economy over time. This complex interplay continues today.

Conclusions

In summary, Edison has a long and dynamic geologic history stretching back over 1 billion years. A variety of ancient Precambrian igneous, metamorphic and sedimentary formations underlie the town, later deformed by continental collisions. More recent glaciations during the ice ages eroded and deposited extensive sediments still shaping the landscape today.

Ongoing fluvial processes along the Raritan River basin and seismic activity amid fault zones continues to influence Edison’s geology as well. These factors have impacted not just the land itself but also ecology, hydrology, economic development, hazards mitigation, and human settlement patterns across the town for centuries.