Geoscience Reference
In-Depth Information
II
III
III
II
I
I
II
III
III
IV
IV
Equator
IV
V
V
VI
I—II Transition
(i)
(ii)
100
50
(iii)
0
-50
(iv)
-100
(v)
-10,000
0
I Glacial unloading
coastal emergence
II Collapsing forebulge
coastal submergence
200
200
Sea-level
curve
m
m
-50
100
-100
0
-10,000
0
-10,000
0
III Eustatic submergence
IV Oceanic submergence
Pacific coast ranges, southern California.
Photo: Ken Addison
0
0
m
m
-50
-50
100
-10,000
0
-10,000
0
V Oceanic submergence
VI Oceanic margin emergence
Deltas extend the coastline most obviously where tide
and wave energy are low, in protected shelf seas, and do
little to reshape the delta. The modern Mississippi river
forms a classic elongated, fluvially dominated delta where
it enters the hurricane-prone, but otherwise sheltered,
Gulf of Mexico. Increasing wave action arrests the delta
front nearer the regional coastline. Transverse bars become
more prominent, developing onshore to form an
interrupted barrier coastline (see below) damming tidal
lagoons to their rear. Tide-dominated deltas are subject
to tidal inundation and low-tide drainage through the
distributary channel network and surface saltwater
flooding of the delta plain. The higher the tidal range, the
more the landward water and sediment fluxes of incoming
tides constrain the seaward development of the delta.
The delta landsystem is a three-dimensional mosaic of
individual channel, plain, lagoon, salt-pan and barrier
landforms with wide-ranging sediment calibres. Channel
meandering, storm events and fluctuating sea levels create
ever-changing surface patterns. Delta plain surfaces are
+4m
0
+2m
0
m
m
-50
-50
-10,000
0
-10,000
0
Years
Figure 17.10
Global zones of probable sea-level variations
isostatic recovery; II, Ice sheet periphery zone; I-II transition,
complex ice sheet margins experiencing both isostatic and
eustatic changes, and particularly appropriate for Britain; III,
eustatic submergence beyond ice limits; IV-VI, regimes of
oceanic submergence/emergence.
Source: After Clark et al.(1978)
