310
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
the region not long ago; such a structure, similar to a niche glacier with a push-moraine, was
found in the upper reaches of one of the Scalisty stream tributaries.
.
In postglacial time the lake was finally separated from an extensive shallow water reservoir.
In the intermountain depression of the northern lakeshore, the large lacustrine-alluvial terrace
was generated, on which peat accumulated; the accumulation rate, however, was very low and
the current peat depth is not more than 0.5 m. Formation of the ice-lode and of polygonal
microrelief occurred simultaneously. The presence of peat-paisa bogs, which cannot be
generated under modern conditions in Central Taimyr, indicate a probably gradual drainage.
Such bogs are described on the northern coast of Ledjanaja Bay and their azonality is
emphasized by a lush dwarf bush (Betula nana) growth, which is currently dominant of more
southern tundra. The low pebbly lake terraces drained last. Based on indirect attributes of the
terraces, the drainage occurred against a background of climatic cooling: higher elevation
polygonal networks are large. Of modern geomorphologic processes, alluvial, permafrost
(more detailed description given below), erosional and deluvial (scree processes) are the most
advanced. It is interesting that erosional processes in the cleft of the left hand tributary of the
Mramornaja river are rather active, where the annual accumulation of rough sediments reaches 1
m in some places. The general relief in the region is middle mountainous (the term "middle
mountainous" is used here to indicate altitudinal zonation). The range of relief features
decreases with increasing distance from the lake basin. On the north-west lakeshore the relief
amplitude attains 400 m, to the north-west of the basin, 100-150 m, and to the north, not more
than 50 m.
The mountain structures usually have a table shape, with abrupt slopes and flat tops. At
higher elevations the slopes are frequently terraced by nival altiplanation and structural terraces
and are complicated by outcrops of dolerite and other intrusions resistant to weathering. The
auleurolites are pelitisated to gravel and smaller-sized material. Downslope, profile development
of cryogenic micro- and nanorelief is intensified. The valleys of the small mountain rivers
usually have V -shaped or U-shaped transverse sections, sometimes canyon-shaped
(Mramomaja river, Vodopadny stream). The corresponding rivers have no more than 2 fluvial
levels: low and high flood-plain. In the majority of cases alluvial deposits are not differentiated.
Deluvial accumulation occurs only on the periphery of the mountain lake kettles. At one
location, significant displays of thaw slumping (gelifluction) are observed.
The large valleys and small valley mouths have 3-4 alluvial levels: usually low and high
flood-plain, and terrace. The lake terraces were described earlier. In the bogs, thermokarst
processes are very intense, and there are several thaw lakes, of which the largest is about 0.7
km 2 .
Permafrost, cryomorphogenetic processes and cryogenic relief
The lake basin is in the zone of continuous permafrost and under rather severe conditions. The
permafrost reaches to a depth of 500 m and a temperature of -13
D
C (Geocryologie of USSR,
1989). The depth of seasonal ground thaw ranges from 20-25 cm in peat up to 1 m in gravelly
soil without vegetation. Under these conditions, cryogenic processes are the leading factor in
determining the structure and functioning of geosystems. Practically all important cryogenic
processes, except pingo formation, are displayed within the Levinson-Lessing Lake basin. It is
most expedient to consider them together with consequent cryogenic relief forms. We do not
adhere to any of the existing classification systems for cryogenic processes and forms;
however, as a basis for their characterization, we use the genetic classification of B.I.Vtiyrin
(1969), and the morphological classification system of A.L.Washbum (1979,1988).
Only seldom does any cryogenic process occur alone. They generally occur in conjunction
with non-cryogenic morphogenetic processes: aeolian, alluvial and other processes. The
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
the region not long ago; such a structure, similar to a niche glacier with a push-moraine, was
found in the upper reaches of one of the Scalisty stream tributaries.
.
In postglacial time the lake was finally separated from an extensive shallow water reservoir.
In the intermountain depression of the northern lakeshore, the large lacustrine-alluvial terrace
was generated, on which peat accumulated; the accumulation rate, however, was very low and
the current peat depth is not more than 0.5 m. Formation of the ice-lode and of polygonal
microrelief occurred simultaneously. The presence of peat-paisa bogs, which cannot be
generated under modern conditions in Central Taimyr, indicate a probably gradual drainage.
Such bogs are described on the northern coast of Ledjanaja Bay and their azonality is
emphasized by a lush dwarf bush (Betula nana) growth, which is currently dominant of more
southern tundra. The low pebbly lake terraces drained last. Based on indirect attributes of the
terraces, the drainage occurred against a background of climatic cooling: higher elevation
polygonal networks are large. Of modern geomorphologic processes, alluvial, permafrost
(more detailed description given below), erosional and deluvial (scree processes) are the most
advanced. It is interesting that erosional processes in the cleft of the left hand tributary of the
Mramornaja river are rather active, where the annual accumulation of rough sediments reaches 1
m in some places. The general relief in the region is middle mountainous (the term "middle
mountainous" is used here to indicate altitudinal zonation). The range of relief features
decreases with increasing distance from the lake basin. On the north-west lakeshore the relief
amplitude attains 400 m, to the north-west of the basin, 100-150 m, and to the north, not more
than 50 m.
The mountain structures usually have a table shape, with abrupt slopes and flat tops. At
higher elevations the slopes are frequently terraced by nival altiplanation and structural terraces
and are complicated by outcrops of dolerite and other intrusions resistant to weathering. The
auleurolites are pelitisated to gravel and smaller-sized material. Downslope, profile development
of cryogenic micro- and nanorelief is intensified. The valleys of the small mountain rivers
usually have V -shaped or U-shaped transverse sections, sometimes canyon-shaped
(Mramomaja river, Vodopadny stream). The corresponding rivers have no more than 2 fluvial
levels: low and high flood-plain. In the majority of cases alluvial deposits are not differentiated.
Deluvial accumulation occurs only on the periphery of the mountain lake kettles. At one
location, significant displays of thaw slumping (gelifluction) are observed.
The large valleys and small valley mouths have 3-4 alluvial levels: usually low and high
flood-plain, and terrace. The lake terraces were described earlier. In the bogs, thermokarst
processes are very intense, and there are several thaw lakes, of which the largest is about 0.7
km 2 .
Permafrost, cryomorphogenetic processes and cryogenic relief
The lake basin is in the zone of continuous permafrost and under rather severe conditions. The
permafrost reaches to a depth of 500 m and a temperature of -13
D
C (Geocryologie of USSR,
1989). The depth of seasonal ground thaw ranges from 20-25 cm in peat up to 1 m in gravelly
soil without vegetation. Under these conditions, cryogenic processes are the leading factor in
determining the structure and functioning of geosystems. Practically all important cryogenic
processes, except pingo formation, are displayed within the Levinson-Lessing Lake basin. It is
most expedient to consider them together with consequent cryogenic relief forms. We do not
adhere to any of the existing classification systems for cryogenic processes and forms;
however, as a basis for their characterization, we use the genetic classification of B.I.Vtiyrin
(1969), and the morphological classification system of A.L.Washbum (1979,1988).
Only seldom does any cryogenic process occur alone. They generally occur in conjunction
with non-cryogenic morphogenetic processes: aeolian, alluvial and other processes. The