Geoscience Reference
In-Depth Information
Figure 8-9.
Bolstadfjord, near Bergen in western Norway. A. Overview looking toward the fjord entrance under the
bridge at center distance. Water depth in the foreground is several hundred meters. B. Close-up view of bridge over
the fjord entrance. Tidal l ow creates ripples in the water surface over the threshold, which is only a few meters
deep. This fjord basin is barely connected to the marine environment at present. Photos by J.S. Aber.
Figure 8-10.
Use of a small basin in hard bedrock to establish the time of emergence above sea level during
postglacial rebound of the crust. M
fresh water. Date of the top brackish sediment marks
the time of threshold uplift above sea level. Adapted from Anundsen, K. 1985. Changes in shore-level and ice-front
position in Late Weichsel and Holocene, southern Norway.
Norsk Geograi sk Tidsskrift
39, p. 205-225, Fig. 2.
=
marine, B
=
brackish, F
=
of the fjord-head region (emergence) and
drowning of the shelf area (submergence).
The Mississippi River delta exhibits another
complicated situation for isostasy and eustasy
(Fig. 8-13). During times of major glaciation,
when sea level was low, the Mississippi River
incised a deep valley across the delta and
transported sediment into the Gulf of Mexico
well beyond the delta. During interglacial times,
in contrast, high sea level allowed sediment
accumulation, ini lling of the valley, and growth
of the delta. These substantial changes in sedi-
ment mass of the delta induced crustal subsid-
ence and rebound exceeding 9 m (30 feet) along
