Introduction
• ”Relief and landforms in Finland from the
point of topographic mapping”
This lecture consists of
• General terminology
• Connection between bedrock and landforms
• Relief types
• Present geomorphologic processes
Terminology
•
Topographic map - a presentation of the external features (morphography) of
landforms but not a perfect one.
•
Geomorphologic map – A map depicting selected terrain features.
•
Geomorphology - The study of the form of the ground surface and the processes which
shape it.
•
Geography - The study of the Earth’s surface.
•
Geology - The study of the solid Earth.
•
•
Surficial deposits - Quaternary deposits – Overburden
- Loose unconsolidated material resting on bedrock.
Bedrock - Unweathered rock beneath unconsolidated material.
1
Distribution of Surficial deposits
•
•
•
•
•
•
•
•
•
•
Rocky terrain
13.4
Boulder deposits
0.5
Basal till
48.2
Hummocky moraine 5.1
Eskers and ice-marginal formations
5.0
Valley trains
1.8
Clay deposits
8.3
Littoral deposits
1.3
Fluvial deposits
0.9
Peat deposits
15.5
2
Polygenetic erosional relief of
bedrock
•
The effect of endogenic phenomena has been considerable in relief forming,
including:
- orogeny; formation of mountain ranges, folding and block movement
- volcanism; volcanic activity
- unorogenic crystallization of magma in Earth's crust
- earthquakes
•
The effect of exogenic processes too:
- Land uplift; in places about 200m since the end of glaciation
- Meteorites; causing chock metamorphism ( 9 cases in Finland, e.g. the lake
Lappajärvi crater)
- Ice age; peeled the bedrock to the Unweathered surface (seen as roches
mountonees)
- Weathering; physic w. ( freezing - warming up) most significant of the
processes in Finland. Chemical w. not very significant in our conditions.
3
Rock types and landforms
• In addition to plutonic rocks, coherent schist belts occur in
our area. They are made of metamorphosed sediments;
clay and volcanic rocks by melting and recrystallizing.
• Sedimentogenic rocks; sandstones, claystones and
limestones are very rare.
• Our land area can be divided into different Lithological
regions having effect on present-day landforms (e.g.
M.Seppälä 1986).
4
5
Finnish bedrock
• Mainly composed of crystalline plutonic rocks;
granites and gneisses.
• Part of the Fennosarmatian Precambrian block
of northern and eastern Europe, which is exposed
from beneath the overlaying sedimentary rocks in
Fennoscandia and in Ukrainian.
• In general overburden is thicker in low-laying,
flat areas than in areas of varying rock relief.
6
7
Slope terminology
• A -Free face; The steepest part of a slope profile with an arbitrary
minimum slope angle of 45 deg.
-Scree slope; An accumulation of fragmented rock waste below a
cliff.
• B -Mountain front; A portion of the land surface rising considerably
( > 600 m) above the surrounding country.
-Pediment; A gentle slope (gradient < 10 deg.) occurring below a
markedly steeper slope.
• C - Concave slope; A sloping terrain in which the gradient becomes
progressively gentler when going downwards the slope.
• D -Convex slope; A sloping terrain in which the gradient becomes
progressively steeper when going downwards the slope.
• E -Rectilinear slope; A slope, or part of a slope which has a constant
angle.
8
9
Fracture lines and relief
•
Finnish bedrock is fractured with fissures (open breaks in rock), joints
(fractures in a rock which exhibit no differentia movements) and faults
(fracture of rock strata due to strain with observable displacement) - Bedrock
is split up into blocks.
-Faults are rare in Finland. Most of our lake basins occupy fracture valleys.
-Strike of schistosity does not affect landforms as markedly as fractures do.
Physical weathering - mechanical wear, variations in temperature, freezing
water and biotic factors leads to continuous reduction of the rock fragments.
-Our rocks with abundant silica are highly resistant to chemical weathering.
-As a whole the land surface of Finland is almost flat - peneplain. The
exception: Narrow Caledonian mountain range of Scandinavian in the
northwest of Lapland.
10
11
Fissuring types
• Each rock type has its own characteristics of fissuring:
• Elevations in plutonic silicic granite regions e.g. are rounded hills,
owing to three perpendicular jointing planes of this rock type; we are
talking about cubic fissuring.
• Wedgy or composite fissuring is typical for mafic rocks (rich in
magnesium and iron; often dark in colour; e.g. gabbro, diabase) and
migmatites.
•
Platy fissuring characterizes metamorphosed rock areas (schists,
phyllites, gneisses).
• Vertical fissuring comes often down to the depth of 100 m.
12
Abundance of main rock types
(After J. Sederholm)
•
•
•
•
•
•
•
Silicic plutonic rocks
52.5 %
Migmatites
21.8
Schists
9.1
Mafic igneous rocks
8.2
Quartzites and sandstones4.3
Granulites
4.0
Limestones
0.1
Glacigenic relief
•
•
•
•
Erosional forms; created when the glacier advanced
- Various stoss and lee sides of rocky hillocks caused by glacial erosion
-Roches moutonnees with various striaes, grooves and chatter marks
-Chute-like longitudinal valleys.
•
Depositional landforms; contain till material accumulated under the ice, on the top
of it and at its margins
- Ground moraine
- Drumlins and drumlin fields; ridges consisting of till, parallel to glacier flow
- Ice-marginal formations; e.g. I-III Salpausselkä
- Terminal or end moraines; e.g. De Geer moraines
- Hummocky-, Glacialkarst-, Pulju-, Plateau-, Rogen-moraines
- Ablation till i.e. loose melt-out till; complex topography of hummocks and kettles
13
14
15
Glaciofluvial relief
• Eskers; Sediment deposited on the bottom of melt water streams
• Glaciofluvial deltas; Occur where melt water streams ended in deep
water
• Kames; Cone-shaped, roundish formations occurring in swarms
• Sandurs; Outwash plains accumulated on freshly emergent surface of
deltas
• Kettle terrain; Occurring often on deltas made by melted ice blocks
• Lateral drainage channels; Cut by running water into the fell slopes
• Kame terraces; Deposited between a stagnant ice and the wall of a
valley
16
Introduction
• ”Relief and landforms in Finland from the
point of topographic mapping”
This lecture consists of
• General terminology
• Connection between bedrock and landforms
• Relief types
• Present geomorphologic processes
17
Glaciofluvial relief
• Eskers; Sediment deposited on the bottom of melt water streams
• Glaciofluvial deltas; Occur where melt water streams ended in deep
water
• Kames; Cone-shaped, roundish formations occurring in swarms
• Sandurs; Outwash plains accumulated on freshly emergent surface of
deltas
• Kettle terrain; Occurring often on deltas made by melted ice blocks
• Lateral drainage channels; Cut by running water into the fell slopes
• Kame terraces; Deposited between a stagnant ice and the wall of a
valley
18
19
20