Transcript Virginia Geologic History and Regions - pams

Virginia Geologic History and
Regions
Take a look at cities you might have visited
• There are 5 regions…. These are on your
notes sheet provided to you
Coastal Plain
• Youngest sedimentary rocks in VA
• Low topographic relief:
– Elevation on land: 0-300 ft
– Lands slopes east under the Atlantic
Ocean & forms continental shelf; extends
200 miles offshore
Coastal Plain
continued
• Swamps: Great
Dismal Swamp
• Bays (Chesapeake)
& estuaries
• Extends westward to
the “fall line”
Piedmont
Profile of the James River across
the Fall Zone
Elevation
• Rolling landscape
• Slopes eastward from
1000ft to 300ft in the
east
• Weathering over long
time has produced
soils 150ft deep
• Metamorphic, igneous,
& sedimentary rocks
present
Distance from source
Blue Ridge
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Long & narrow region
Elevations between 2300ft & 3200ft
Highest peak: 5719ft
Metamorphic & igneous
Valley and Ridge
• Large valley:
Shenandoah & other
narrow, parallel valleys
• Valleys in SW are
1000ft or higher than
in NE valleys
• Folded Appalachians
• Sedimentary:limestone
Reported or known caves in
Virginia
Appalachian Plateau
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SW part of state
Flat high elevations
Sedimentary rocks (coal)
Drained by Tennessee
River (to the W)
Observe the watersheds
On the next slides…
Read each slide
Copy what is underlined
Virginia’s Geologic History
Virginia is unique
because it has:
Mountains
Hills and valleys
foothills
Sandy beaches…
All in 1 state!!
1 bya (billion years ago)
• VA was a little chain
of volcanoes where
the Blue Ridge
Mountains are
today
• Everything else was
underwater
500 mya (million years ago)
• Still underwater and a chain of volcanoes
• Coastline located where valley and ridge are
today
• VA located S of the equator, had a tropical
climate
• Sediment was deposited over western VA, shells
and coral were deposited, which explains the
presence of
sedimentary rock in the
V & R (valley & ridge) and
A.P. (appalachian plateau) regions
225 mya
Africa collided with
North America, collision
hard enough to wrinkle
up the crust under the
inland sea west of the
Blue Ridge
“wrinkles” formed the
Appalachian mountains
continued
The mountains were 15,000 to 20,000 ft,
largest in the US (at that time)
Force of collision produced heat and
pressure which changed some sedimentary
rocks of limestone into marble
190 mya African plate started to pull away
and the Atlantic opened, the pulling caused
the land west of Richmond to stretch and
crack, erosion caused these rift valleys to fill
with mud and clay
140 to 70 mya
 Sediment from the eroding Appalachian
mountains gets carried across the
Piedmont by streams and rivers which
washes into the Atlantic Ocean
 Coastline is now located where
Richmond is today
 Over millions of years, sediments
continued to build up which formed the
Coastal Plain
… the sand on the beaches is actually
rocks from the Appalachian Mountains
Ice Age-1.8 mya
o Due to cold temps ice piled up in Canada and
northern US
o Ice sheets covered areas of North America,
including parts of VA
o Much of the water evaporated and the sea
level was 450ft lower than today, VA coastline
was 60 miles farther to the East
o As glaciers melted sea level rose rapidly