Shorelines and Shoreline Processes - The Changing Earth: Exploring Geology and Evolution - page 422

V + Sediment added from erosion by longshore transport onto beach
V - Sediment carried down-coast from the beach by longshore transport
W - Sediment blown inland by wind
O - Sediment cascading down the submarine slope
(V + ) + (V - + W - + O - ) = 0

INPUT
OUTPUTS

STABLE BEACH:

River

Inland
dunes

V +

W -

Beach

V -

O -

Submarine landslide

◗ Figure 16.15 The Nearshore Sediment Budget The long-term sediment budget can be assessed by
considering inputs versus outputs. If inputs and outputs are equal, the system is in a steady state, or
equilibrium. If outputs exceed inputs, however, the beach has a negative budget and erosion occurs.
Accretion takes place when the beach has a positive budget with inputs exceeding outputs.

irregular and typically lack well-developed beaches, except
in protected areas (see Geo-inSight on pages 424 and 425).
They are further characterized by sea cliffs, wave-cut plat-
forms, and sea stacks. Many of the coasts along the West
Coast of North America fall into this category.
The following section will examine coasts in terms
of their changing relationship to sea level. But note that
although some coasts, such as those in southern California,
are described as emergent (uplifted), these same coasts may
be erosional as well. In other words, coasts commonly possess
features that allow them to be classifi ed in more than one way.
Submergent and Emergent Coasts
If sea level rises with respect to the land or the land sub-
sides, coastal regions are fl ooded and said to be submergent
or drowned coasts (

Carolina was fl ooded during the rise in sea level following
the Pleistocene Epoch, so it is extremely irregular. Recall
that during the expansion of glaciers during the Pleistocene,
sea level was as much as 130 m lower than at present, and
that streams eroded their valleys more deeply and extended
across continental shelves. When sea level rose, the lower
ends of these valleys were drowned, forming estuaries such
as Delaware and Chesapeake bays (Figure 16.16). Estuaries
are simply the seaward ends of river valleys where seawater
and freshwater mix. The divides between adjacent drainage
systems on submergent coasts project seaward as broad
headlands or a line of islands.
Submerged coasts are also present at higher latitudes
where Pleistocene glaciers fl owed into the sea. When sea level
rose, the lower ends of the glacial troughs were drowned,
forming fiords (see Chapter 14 Geo-inSight on pages 370
and 371).

Figure 16.16). Much of the East Coast
of North America from Maine southward through South

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