Geological structure: platforms
The Earth's crust is made of blocks. A platform is a very old, flat and steady block. It has two parts: a hard crystalline base at the bottom, and a cover of layered sediments on top. Where the base reaches the surface it is called a shield.
- East European Platform: very old base, gentle plain on top (the Russian Plain). The shield shows in the north-west (Kola and Karelia).
- Siberian Platform: very old, rises into the Central Siberian Plateau.
- West Siberian Plate: a young platform; its old base is buried deep under thick sediments, so the land is a vast flat lowland.
Mountain belts and relief
When two blocks of crust push together, the layers between are squeezed and folded. The ground rises into a fold belt. The age of the folding decides the height.
- Urals: very old (Palaeozoic) folds. They are worn down and low (highest about 1,900 m).
- Altai and Sayan, Baikal region: older folds that were lifted again later.
- Verkhoyansk-Chukotka and the Pacific belt (Kamchatka, Kurils, Sakhalin): young Mesozoic and Cenozoic folds, high and active.
- Caucasus: young Alpine folds. Mount Elbrus (5,642 m) is the highest peak.
So: platforms give plains and plateaus; fold belts give mountains. Rivers and ice then shape both.
Geochronology: reading rock age
Geochronology puts the Earth's history on a time ladder (from oldest to youngest):
- Precambrian (before 540 million years ago): the oldest hard rocks, the platform bases.
- Palaeozoic (540 to 250 million years ago): old folding, like the Urals; coal forests.
- Mesozoic (250 to 66 million years ago): folding in the north-east; many sediments.
- Cenozoic (from 66 million years ago): the youngest folding, the Caucasus and the Pacific belt.
The rule of thumb: the older the folding, the lower and rounder the mountains.
Minerals and hazards
Minerals follow geology.
- Sediment cover: coal, oil, gas, salts, building sand. For example, oil and gas in West Siberia; coal in Kuzbass and the Pechora basin.
- Hard base: iron ore (for example the Kursk magnetic anomaly), apatite, nickel and diamonds in old rocks.
- Fold belts: metal ores (copper, gold, tin, polymetals), for example in the Urals and the east.
Hazards: Earthquakes and volcanoes happen where crust is young and moving: Kamchatka (a volcano such as Klyuchevskaya Sopka, about 4,750 m, is still active), the Kurils, Sakhalin, the Caucasus and the Baikal region. Platforms are quiet. Mountains also have avalanches, landslides and mudflows.
Key formulas and definitions
- Platform = hard old base + sediment cover โ plains and plateaus
- Fold belt = crust squeezed and folded โ mountains
- Age order: Precambrian โ Palaeozoic โ Mesozoic โ Cenozoic
- Older folds = lower, rounder mountains; younger folds = higher, sharper, more earthquakes
Worked examples
1. Why are the Urals much lower than the Caucasus?
The Urals folded in the Palaeozoic, about 300 million years ago, and have been worn down by wind, water and ice. The Caucasus folded in the Cenozoic, so it is young and high.
2. Where would you drill for oil: on a platform with thick sediments or in a young fold belt?
On a platform with thick sediments. Oil and gas form in layered sediments, like those of the West Siberian Plate.
3. A plain is flat, old and has thick layers on top. What is below it?
A platform: a hard crystalline base with a cover of sediments.
4. Why does Kamchatka have volcanoes but the Russian Plain does not?
Kamchatka lies on a young, moving fold belt at the Pacific edge. The Russian Plain is a steady old platform where the crust is quiet.
Common mistakes
- Thinking mountains are always the oldest part. Old mountains are low; young ones are high.
- Putting oil and gas in the hard base. They fill the sediment layers.
- Mixing up platform (flat, steady) and fold belt (crumpled, mountains).
- Forgetting that earthquakes and volcanoes follow young belts, not old platforms.