Environmental Engineering Reference
In-Depth Information
MSL
Chesapeake Bay
15
Very soft
organic
silt
30
Soft gray organic silt
45
Erode
d surface,
(overlying so
ils
r
ec
ent alluvium)
Alluvial sands
60
Cretaceous clayey sands
75
2000 m
FIGURE 7.37
Geologic section in channel area of Chesapeake Bay between Kent Island and Sandy Point. A drowned river
valley. (After Supp, C. W. A.,
Engineering Geology Case Histories
1-5, Trask, P. and Kiersch, G. A., Eds., Geological
Society of America, New York, 1964, pp. 49-56.)
Palisades
diabase
(traprock)
Artificial fill
MSL
10
20
30
40
50
60
70
80
Hudson River
Triassic
sandstones
and shales
Soft organic silts interbedded with sands
Fluvial-glacial
silts, sands,
and gravels
Eroded bedrock surface
1200 m
FIGURE 7.38
Geologic section, Lincoln Tunnel, west shore (New Jersey). A drowned river valley. (From Sanborn, J.,
Engineering Geology
[Berkey Volume], Geologic Society of America, 1950, p. 49. With permission.)
7.4.3
Coastline Environment
Classification of Coastlines
Emergent and Submergent Coasts
Since the Pleistocene, the elevations of many coastlines have been changing, some even fluc-
tuating. In general terms, they may be classified relative to sea level as rising (emergent),
subsiding (submergent), or stable. The general conditions of the coastlines of the world are
given in
Figure 7.42.
Erosion dominates emergent coastlines and deposition dominates sub-
mergent coastlines. The landform expressions indicate the soil conditions to be anticipated,
since they reflect whether erosional or depositional processes are occurring.
Modern coastlines are primarily the result of the activity of the Pleistocene glaciers. The
Earth's crust deflected beneath their huge masses and then, as they melted, crustal
rebound occurred, and is still active today in the extreme northern and southern hemi-
spheres. Simultaneously with rebound, the glacial ice melted, causing the sea level to rise
as much as 300 ft. In many areas around the middle latitudes sea levels are still rising and
