Environmental Engineering Reference
In-Depth Information
Figure 1
Tectonic and macromorphological character of the global
coastline.
Source: After Inman and Nordstrom (1971).
Emergent and submergent
trends identify relations between global sea level and
coastlines over particular time scales. The most relevant context today is one of
Quaternary glacio-eustatic fluctuations, superimposed on an overall tectono-eustatic sea-
level fall of 100-200 m. Ocean-ice coupling, capable of ± 250 m of eustatic sea-level
change if all ice were to melt and reform, has a major impact on continental margin
systems of similar relief range. It accounts for marine transgression and regression
throughout the Pleistocene. This has fallen short of the full rate, since major ice sheets
have survived temperate stages, and is complicated by glacio-isostatic response (see
Chapter 11). These mechanisms are evident in global patterns of response during the past
15 ka (see Figure 2). Submergence has flooded river valleys (
rias
) and created
structurally discordant fjord coasts in intensely glaciated areas of Norway, west Scotland
and the South Island of New Zealand (see Plate 15.12). By contrast, emergence leaves
coastal landforms, especially
raised beaches
, abandoned cliffs and platforms, stranded
above the contemporary coastline (see Plate 17.6). The British Isles straddle Zones I-II to
provide a microcosm of submergent and emergent coastlines (see Figure 3). Human-
forced global warming is now set to ornament these larger trends through sea level rise
