620
Climatic Geomorphology
columns from the centre of China (Porter and Zhisheng, 1995), glacial deposits in western
USA (Clark and Bartlein, 1995), and with sequences of talus flatirons in northeastern Spain
(Guti6rrez et al., 1998b). All this seems to indicate that there is a global climatic influence
of the effects of the Heinrich events, at least in the Northern Hemisphere.
3. Fluctuations of quaternary ice sheets and resulting landforms
The advances and recessions of the glaciers have a bearing on morphogenesis, so it is
fundamental to know accurately the oscillations that occurred in order to understand
the resulting glacial landscape. These glacial landforms are produced by erosion and sedimentation processes and crop out when ice masses retreat. On the basis of existing
landforms, areas and flow directions of the ice in ice sheets have been calculated.
The maximum expansions of the last ice sheets have a similar age. Dawson (1992),
compiled global data that indicate an age of 15,000 to 20,000 years for the Euroasiatic
ice sheet (late Valdai), 18,000 to 20,000 years for the Fennoscandian (late Weichselian),
for the Laurentide ice sheet 20,000 to 25,000 years (late Wisconsin), and for the Antarctica
ice sheet 17,000 to 21,000 years. The distribution of glaciers and icecaps for the last glacial
maximum, with variations of the equilibrium line depending on the latitude and altitude,
are shown in Figure 24.4 (Broecker and Denton, 1990).
The warming subsequent to the glacial maximum caused the disappearance of the
Eurasian, Fennoscandian, and Laurentide ice sheets, and many valley glaciers and small
glacier caps. The response can be observed in the data that show the modification of the
general circulation of the atmosphere, in the rise of the sea due to the incorporation of
fresh water, and thus, in the modification of the oceanic circulation. Melting events are
not synchronous; the Cordilleran ice sheet disappeared 10,000 years ago, the Laurentide
ended 6500 years ago, the Fennoscandian melted about 8000 yr BP, and the Eurasian had a
shorter life, 9000 yr BP (according to some authors, in Dawson, 1992).
It is difficult to establish a chronology for the Fennoscandian ice sheet due to the fact
that moraines are very broken and cannot be properly correlated in fiord areas. After
13,000 yr BP, a rapid slimming and retreat occurred, which corresponds to a warm interstadial that lasted until 11,000 yr BP. In southern Scandinavia a big lake was formed
between northern Europe and the southern part of the ice. This occurred between 12,800
and 10,300 yr BP, and it is called the Baltic frozen lake (Figure 24.5) (Benn and Evans,
1998). About 10,000 yr BP, the retreat of the ice made possible for seawater to come into
the Baltic Sea (Yoldia Stage). After that, there was a rapid recession of the ice, between
10,000 and 9000 yr BP, so that the ice sheet was reduced to a small extension in northern
Sweden and a big fresh water lake was originated (Ancylus Lake). Finally, and probably
due to the glacioisostatic rebound and to the Flandrian transgression, marine waters went
into the Baltic Sea and Botnia Gulf (Litorina sea).
The Laurentide ice sheet extended from the Canadian archipelago in the Artic Ocean to
the northern states of USA, in the south. It bordered on the Atlantic Ocean to the east and
the Rocky Mountains to the west. From this boundary to the Pacific Ocean, the Cordilleran
ice sheet developed. As a result of the glacioisostatic depression, large proglacial
lakes were originated in the southern part. Ice recession was characterized by sudden
retreats that produced catastrophic floods and spectacular modification of the landscape.
Climatic Geomorphology
columns from the centre of China (Porter and Zhisheng, 1995), glacial deposits in western
USA (Clark and Bartlein, 1995), and with sequences of talus flatirons in northeastern Spain
(Guti6rrez et al., 1998b). All this seems to indicate that there is a global climatic influence
of the effects of the Heinrich events, at least in the Northern Hemisphere.
3. Fluctuations of quaternary ice sheets and resulting landforms
The advances and recessions of the glaciers have a bearing on morphogenesis, so it is
fundamental to know accurately the oscillations that occurred in order to understand
the resulting glacial landscape. These glacial landforms are produced by erosion and sedimentation processes and crop out when ice masses retreat. On the basis of existing
landforms, areas and flow directions of the ice in ice sheets have been calculated.
The maximum expansions of the last ice sheets have a similar age. Dawson (1992),
compiled global data that indicate an age of 15,000 to 20,000 years for the Euroasiatic
ice sheet (late Valdai), 18,000 to 20,000 years for the Fennoscandian (late Weichselian),
for the Laurentide ice sheet 20,000 to 25,000 years (late Wisconsin), and for the Antarctica
ice sheet 17,000 to 21,000 years. The distribution of glaciers and icecaps for the last glacial
maximum, with variations of the equilibrium line depending on the latitude and altitude,
are shown in Figure 24.4 (Broecker and Denton, 1990).
The warming subsequent to the glacial maximum caused the disappearance of the
Eurasian, Fennoscandian, and Laurentide ice sheets, and many valley glaciers and small
glacier caps. The response can be observed in the data that show the modification of the
general circulation of the atmosphere, in the rise of the sea due to the incorporation of
fresh water, and thus, in the modification of the oceanic circulation. Melting events are
not synchronous; the Cordilleran ice sheet disappeared 10,000 years ago, the Laurentide
ended 6500 years ago, the Fennoscandian melted about 8000 yr BP, and the Eurasian had a
shorter life, 9000 yr BP (according to some authors, in Dawson, 1992).
It is difficult to establish a chronology for the Fennoscandian ice sheet due to the fact
that moraines are very broken and cannot be properly correlated in fiord areas. After
13,000 yr BP, a rapid slimming and retreat occurred, which corresponds to a warm interstadial that lasted until 11,000 yr BP. In southern Scandinavia a big lake was formed
between northern Europe and the southern part of the ice. This occurred between 12,800
and 10,300 yr BP, and it is called the Baltic frozen lake (Figure 24.5) (Benn and Evans,
1998). About 10,000 yr BP, the retreat of the ice made possible for seawater to come into
the Baltic Sea (Yoldia Stage). After that, there was a rapid recession of the ice, between
10,000 and 9000 yr BP, so that the ice sheet was reduced to a small extension in northern
Sweden and a big fresh water lake was originated (Ancylus Lake). Finally, and probably
due to the glacioisostatic rebound and to the Flandrian transgression, marine waters went
into the Baltic Sea and Botnia Gulf (Litorina sea).
The Laurentide ice sheet extended from the Canadian archipelago in the Artic Ocean to
the northern states of USA, in the south. It bordered on the Atlantic Ocean to the east and
the Rocky Mountains to the west. From this boundary to the Pacific Ocean, the Cordilleran
ice sheet developed. As a result of the glacioisostatic depression, large proglacial
lakes were originated in the southern part. Ice recession was characterized by sudden
retreats that produced catastrophic floods and spectacular modification of the landscape.