454
cesses, such as the discontinuous storage or loss of large
volumes of detrital sediments in or from their drainage areas. During metastable equilibrium, channel patterns may
9.7
Denudation Rates, Summary
The effects of relief, climate and, to some extent,
the influence of soils and vegetation on (natural)
denudation rates are summarized in Fig. 9.14.
- Lowlands under wet climate with vegetation and
high runoff tend to display more chemical than
mechanical denudation. Furthermore, chemical
denudation rates depend largely on rock types
and hardly at all on relief and can therefore controllandscape evolution.
- Mountainous regions and large drainage areas,
as weIl as entire continents, generally deliver
more (globally by a factor of ca.4) solid than
dissolved load.
- Mechanical denudation of large areas is mainly
controlled by (1) mean local relief or the overall
relief ratio and (2) annual runoff. Regions with
seasonal or rare but heavy precipitation (semiarid to subtropical) may yield as much sediment
as wet tropical zones if their relief is comparable.
- The specific sediment yields or mechanical denudation rates may vary from lowlands to high
mountain areas by 2 to 3 orders of magnitude,
but values for small drainage basins often strongly reflect the erodibility of their dominant rocks
Chapter 9 Denudation and Mass Transport
change from straight and braided to sinuous; slopes may
retreat, become gentier, and evolve from convex to a more
concave form.
and may therefore deviate from values listed in
Fig.9.14.
- Long-term denudation rates (Table 9.1) largely
confirm the general rules established for the modem world.
- In times of a warm and humid "greenhouse
world" (Sect. 7.8.2) chemical denudation may
have been considerably higher and mechanical
denudation lower than at present.
- In glacial periods and during low sea-level
stands, the sediment yield of the continents was
higher (by a factor of about 2) than presently.
These variations in the global denudation proces ses have to be taken into account when extrapolations into older time periods are undertaken.
- Various human activities have caused the solid
modem river . load to become globally twice or
three times as high as earlier in the Rolocene
(Walling and Webb 1996; Ray 1998).
- Due to isostatic rebound, denudation (or exhumation of buried rocks) is norrnally much greater than surface lowering. As a result, mountain
ranges decay slowly, although they concurrently
deliver huge amounts of sediment into neighboring basins.
cesses, such as the discontinuous storage or loss of large
volumes of detrital sediments in or from their drainage areas. During metastable equilibrium, channel patterns may
9.7
Denudation Rates, Summary
The effects of relief, climate and, to some extent,
the influence of soils and vegetation on (natural)
denudation rates are summarized in Fig. 9.14.
- Lowlands under wet climate with vegetation and
high runoff tend to display more chemical than
mechanical denudation. Furthermore, chemical
denudation rates depend largely on rock types
and hardly at all on relief and can therefore controllandscape evolution.
- Mountainous regions and large drainage areas,
as weIl as entire continents, generally deliver
more (globally by a factor of ca.4) solid than
dissolved load.
- Mechanical denudation of large areas is mainly
controlled by (1) mean local relief or the overall
relief ratio and (2) annual runoff. Regions with
seasonal or rare but heavy precipitation (semiarid to subtropical) may yield as much sediment
as wet tropical zones if their relief is comparable.
- The specific sediment yields or mechanical denudation rates may vary from lowlands to high
mountain areas by 2 to 3 orders of magnitude,
but values for small drainage basins often strongly reflect the erodibility of their dominant rocks
Chapter 9 Denudation and Mass Transport
change from straight and braided to sinuous; slopes may
retreat, become gentier, and evolve from convex to a more
concave form.
and may therefore deviate from values listed in
Fig.9.14.
- Long-term denudation rates (Table 9.1) largely
confirm the general rules established for the modem world.
- In times of a warm and humid "greenhouse
world" (Sect. 7.8.2) chemical denudation may
have been considerably higher and mechanical
denudation lower than at present.
- In glacial periods and during low sea-level
stands, the sediment yield of the continents was
higher (by a factor of about 2) than presently.
These variations in the global denudation proces ses have to be taken into account when extrapolations into older time periods are undertaken.
- Various human activities have caused the solid
modem river . load to become globally twice or
three times as high as earlier in the Rolocene
(Walling and Webb 1996; Ray 1998).
- Due to isostatic rebound, denudation (or exhumation of buried rocks) is norrnally much greater than surface lowering. As a result, mountain
ranges decay slowly, although they concurrently
deliver huge amounts of sediment into neighboring basins.