Virginia Physical Geography - PowerPoint Presentation

Slide1

Virginia Physical GeographySlide2

The Physiographic Provinces of Virginia

Virginia has had a long, complex geologic history, over

1.1 billion

years

Events that have led to the formation of a rich diversity of rocks, and events that have

folded, faulted

and rearranged those rocks in complex patterns.

A physiographic province is a

landform

region, areas divided according to similar terrain that has been shaped by a common geologic history.

Geographers recognize more than 20 physiographic provinces in North America

; five

of these are in the state of

Virginia.Slide3

The Physiographic Provinces of Virginia

Each province is characterized overall by its elevation, relief,

lithology

,

and geologic structure. Because of the region’s history of rock formation, deformation, and

erosion,

specific types of landforms or other geologic features may be associated with a given

province. Slide4

The Physiographic Provinces of VirginiaSlide5

Coastal

Plain

The Coastal Plain is a

flat

area underlain by young, unconsolidated sediments.

Includes

all of Virginia

East

of the

Fall Line

.

The

Fall Line is where Rivers cross from the hard igneous and metamorphic rocks of the

Piedmont

onto the soft roundest rocks in Virginia

.

Deposits of

sand

, silt and clay including marine fossils deposited by rivers.

Layers

of sediment were produced by erosion of the

Appalachian

Mountains and then deposited on the Coastal Plain.Slide6

Coastal Plain

The tilted beds of the Coastal Plain extend offshore some 50 to 75 miles to the edge of the North American continent. During the ice ages of the Pleistocene sea level was lowered, exposing the shelf. Streams flowed across the shelf and carved their valleys into it. One such large valley became Chesapeake Bay when sea levels rose again and flooded the shelfSlide7

Coastal

PlainSlide8

Piedmont

The

Piedmon

t is an area of rolling hills underlain by mostly ancient i

gneou

s and

metamorphic

rocks.

Igneous

rocks are the roots of volcanoes formed during an ancient episode of

subduction

that occurred before the formation of the Appalachian Mountains.

The Piedmont is underlain by

metamorphic

rocks of various origins that were

folded

during the Paleozoic as the North American and African plates converged. Later, in the Mesozoic, it was affected by rifting as Pangaea broke apart and the Atlantic Ocean formed.Slide9

Piedmont

Largest physiographic province.

Bounded on the east by the

Fall Zone

, and on the west by the mountains of the Blue Ridge.

Rolling

topography

, deeply weathered bedrock and rocks are strongly weathered.

Rocks are generally buried under a thick (2-20m) blanket of

saprolite

.

( a chemically weathered rock)

Topography is more rugged closer to the Blue Ridge. Slide10

PiedmontSlide11

Blue

Ridge

The

Blue Ridge

is a high ridge of crystalline rock separating the

Piedmont

from the Valley and Ridge Province.

The

billion-year

old igneous and metamorphic rocks of the Blue Ridge are the oldest in the state.

The

Blue Ridge

province experienced mountain building during the late

Neoproterozoic

era (750-700Ma).

In central and northern Virginia, the 570 million year old

basalts

are over sedimentary rock.

Some metamorphism of these rocks occurred during the formation of the

Appalachian Mountains. Slide12

Blue Ridge

The Blue Ridge is composed of complexly folded and faulted igneous (granitic) and metamorphic rocks. These rocks date to the

PreCambrian

and Paleozoic and represent parts of the basement rock of the North American continent.

When Africa and North America converged during the Paleozoic, these rocks were thrust upward and many miles westward over younger rock materials.Slide13

Blue RidgeSlide14

Valley and

Ridge

Long parallel ridges and valleys of

sedimentary

rock which were folded and faulted, and eroded differently.

540

million

years old

sandstones are overlain by carbonates that make up a region of

limestone

and dolomite.

The

folding and faulting of the sedimentary rocks occurred during a collision between

Africa

and North America.

The

collision, which occurred in the late

Paleozoic

, produced the Appalachian Mountains

.

Carbonates were deposited in a shallow tropical

ocean

along the southeast edge of North America.

Carbonates

in the Shenandoah Valley create the correct environment for caves and sinkholes (

Karst

Topography)Slide15

Valley and RidgeSlide16

Appalachian

Plateau

The

Appalachian Plateau

has rugged irregular topography and is underlain by ancient, flat-lying

sedimentary

rocks.

Large

folds of rock found in the Valley and Ridge become smaller folds and flat-lying rocks in the

Plateau.

Some

parts of the Plateau are relatively flat, and some are hilly and rugged.

The area is actually a series of plateaus separated by faults. The upper layers of the Plateau are rich in mineral resources like

coal, natural gas, and petroleum

.Slide17

Appalachian PlateauSlide18

Watersheds of Virginia

Virginia is drained by three watershedsThe Chesapeake Bay watershed which drain the Northern and Eastern portion of the state This includes The James, Rappahannock, Potomac, & York

The

North Carolina Sounds drain the south central part of the state include the Chowan, and Roanoke

The Mississippi River drains the western part of the state includes the New and Big sandy RiversSlide19

Watersheds of Virginia

Virginia Watersheds