# Mountain Building (Orogeny): Fold, Block, Volcanic & Residual Mountains, Plateaus & Plains (UPSC Geography) Source: https://tracknation.in/story/mountain-building-orogeny-fold-block-volcanic-residual-mountains-plateaus-plains-upsc-geography (TrackNation — free UPSC notes with PYQs) > A UPSC note on orogeny and the Earth's relief features — the four mountain types (fold, block/fault, volcanic and residual), young vs old fold mountains, anticline-syncline and nappe folds, horsts, grabens and rift valleys, isostasy, and the types of plateaus (Tibetan, Deccan) and plains (Indo-Gangetic), with examples and economic significance. Anchors the genuine Mains questions on fold mountains and the Circum-Pacific zone, plus self-MCQs. ## Orogeny — the Process of Mountain Building 🎯 **Exam priority: Important.** *Mountains, plateaus and plains are the relief skeleton of every region — and UPSC asks them both ways. Mains has asked why fold mountains sit at plate margins with earthquakes and volcanoes (2014) and the Circum-Pacific zone (2020); Prelims tests the four-fold mountain classification (2024) and residual ranges of the Peninsula (2026). Know the four mountain types with one or two examples each, the horst-graben pair, and the plateau/plain families.* Stand anywhere on Earth and the land is either high and rugged, broad and flat-topped, or low and level. These three first-order relief features — mountains, plateaus and plains — are built by the **endogenic (internal) forces** of the Earth and then sculpted by erosion. The mountain-building process itself has a name. ## Orogeny — the process of mountain building - **Orogeny is the process of mountain building** by Earth's internal (endogenic) forces — chiefly the compression, folding and faulting of crustal rocks at and near plate boundaries. It is a form of **diastrophism** (deformation of the crust). Diastrophism has two kinds: **orogenic** movements (mountain-building, horizontal/tangential forces — folding and faulting) and **epeirogenic** movements (continent-building, vertical forces — broad uplift or subsidence). - Mountains are classified in two ways. **By location:** continental, coastal, oceanic (mid-ocean ridges). **By mode of formation** — the classification UPSC tests — there are **four types: fold, block (fault), volcanic and residual mountains**. - **Mountains are also dated by orogeny:** geologists name great mountain-building episodes — the very old **Pre-Cambrian** (e.g. the Aravallis), the **Caledonian** and **Hercynian (Variscan)** orogenies of the Palaeozoic (e.g. the Appalachians, Urals), and the recent **Alpine–Himalayan** orogeny of the Tertiary that raised the world's young fold mountains. So a mountain's "age" tells you which collision built it. ## Fold Mountains — the Loftiest, Born at Converging Plates The loftiest mountains on Earth — the Himalayas, the Alps, the Andes — all belong to one family, born of the slow collision of plates. ## Fold Mountains — the loftiest, born at converging plates - **Fold mountains form when thick sedimentary strata are squeezed by compressive (horizontal) forces** at **convergent plate boundaries** and buckled into folds. They are the **highest and longest mountain systems** on Earth. The up-arch of a fold is an **anticline** and the down-fold a **syncline**; with increasing pressure folds become symmetrical → asymmetrical → overfolded → recumbent → **nappe** (a fold thrust bodily over its neighbour, common in the Himalayas and Alps). - **Young fold mountains** are geologically recent and form near **active converging boundaries** — which is exactly why they coincide with the world's **earthquake and volcanic belts** (the basis of the 2014 Mains question). Examples: the **Himalayas** (India–Eurasia collision), the **Alps, Atlas, Andes and Rockies**. The **Circum-Pacific belt** ("Ring of Fire", asked in 2020 Mains) rings these young fold and volcanic mountains with the bulk of global earthquakes. - **Old fold mountains** were raised hundreds of millions of years ago at the plate margins of their time and are now worn low and rounded — e.g. the **Aravallis** (India, among the world's oldest), the **Appalachians** (USA) and the **Urals** (the Europe–Asia divide). - **The Himalayas as a worked example:** the great fold belt runs in three parallel ranges raised by the India–Eurasia collision — the **Greater Himalaya (Himadri)** with the loftiest snow-capped peaks, the **Lesser Himalaya (Himachal)** with hill stations, and the outermost **Shiwaliks** built of the eroded debris of the rising range. Recumbent folds and **nappes** (huge overthrust sheets) are characteristic of this belt — and it is still rising, which is why it is so earthquake-prone. ## Block (Fault) Mountains, Horsts & Rift Valleys Where the crust is pulled apart or snapped rather than squeezed, a very different mountain is born — one made not of folds but of broken, displaced blocks. ## Block (Fault) Mountains, Horsts & Rift Valleys - **Block mountains form when large blocks of crust are broken by faults and displaced vertically** (dip-slip faulting), under either tensional or compressional stress. An **uplifted block bounded by faults is a horst** (the block mountain itself); a **down-dropped block between two faults is a graben**, whose floor becomes a **rift valley**. - **The faults themselves come in types worth knowing:** a **normal fault** (tension pulls the crust apart, one block slips down — builds rift valleys), a **reverse/thrust fault** (compression pushes one block up over another — builds fold-and-thrust mountains), and a **strike-slip (transform) fault** where blocks slide horizontally past each other (e.g. the San Andreas Fault). Block mountains and rift valleys are made mainly by normal (dip-slip) faulting. - Two forms occur: **tilted** block mountains have one steep (fault) scarp and one gentle slope, while **lifted** block mountains have a flat top and steep sides on both flanks. Examples: the **Vosges and Black Forest** flanking the **Rhine rift valley** in Europe, the **Sierra Nevada** (USA), and the **Salt Range** (Pakistan). - **Rift valleys** are the graben counterpart: the **Great African Rift Valley** (the world's largest, from the Red Sea to Mozambique — its horsts include the Mitumba and Ruwenzori ranges) and, in India, the **Narmada and Tapi** rivers, which flow westward in rift valleys (graben) between horst blocks — the reason they do not build deltas. ## Volcanic & Residual Mountains, and Isostasy The last two mountain families are built by fire and unmade by erosion. ## Volcanic & Residual Mountains - **Volcanic mountains are built by the accumulation of erupted material** — lava, ash, cinders and volcanic bombs piling up in successive layers around a vent to form a cone — so they are also called **"mountains of accumulation"**. They cluster along the Circum-Pacific belt. Examples: **Mt. Fuji** (Japan), **Mt. Mayon** (Philippines), **Mt. Kilimanjaro** (Africa, the highest free-standing volcanic mountain) and **Mt. Etna** (Italy). - **Residual (relict) mountains are the eroded survivors of once-higher fold, fault or volcanic mountains** — what is left after denudation has stripped most of the original range away. Examples: the **Aravallis, Nilgiris, and the Eastern & Western Ghats** in India, and the **Monadnocks** of the USA (an isolated residual hill is itself called a *monadnock*). The Peninsular Block's residual ranges (e.g. Velikonda, Mahendragiri) were tested in **Prelims 2026**. - **Isostasy** — the buoyant balance ("floating") between the lighter crust and the denser mantle beneath — governs all of this: when erosion strips a mountain or ice melts off it, the lightened crust slowly **rises (isostatic uplift)**; when sediment or ice loads it, the crust **subsides**. It is why eroded mountains keep re-rising and why deep roots underlie high ranges. | **Mountain type** | **How it forms** | **Examples** | | Fold | Compression of sedimentary strata at converging plates | Himalayas, Alps, Andes (young); Aravallis, Appalachians (old) | | Block (fault) | Vertical displacement of crustal blocks by faulting (horst/graben) | Vosges & Black Forest, Sierra Nevada, Salt Range | | Volcanic | Accumulation of erupted lava and ash around a vent | Fuji, Mayon, Kilimanjaro, Etna | | Residual | Erosional survivors of older mountains (denudation) | Aravallis, Nilgiris, Monadnocks | ## Plateaus & Plains — the Other Relief Features Between the mountains lie the other two great relief features — the broad uplands and the level lowlands where most people actually live and farm. ## Plateaus & Plains — the other relief features - A **plateau is an elevated upland with a relatively flat top and steep sides** ("tablelands"). Main types: **tectonic / intermontane** plateaus enclosed by mountains (the **Tibetan Plateau**, the highest and largest in the world); **volcanic / lava** plateaus built of flood basalt (the **Deccan Plateau**, Columbia–Snake); **continental** plateaus rising from plains or coasts; **piedmont** plateaus at the foot of mountains; and **dissected** plateaus cut up by rivers. Plateaus are storehouses of minerals (the Deccan's iron, manganese, coal — Mains 2022 asked the Deccan Trap's resource potential). - A **plain is a low, flat or gently rolling lowland**, usually below ~200 m. By origin: **structural** plains (uplifted sea floor), **erosional** plains (worn down by rivers, ice or wind to a near-level *peneplain*), and **depositional** plains — the most fertile and densely settled — built by deposition, such as river **alluvial plains** (the **Indo-Gangetic Plain**), glacial, lacustrine and coastal plains. Depositional plains carry the world's farming and population. ## Why this matters for UPSC - Prelims tests the **four-fold mountain classification**, the **horst–graben** pair and matched examples (2024); Mains asks **why fold mountains sit at plate margins with earthquakes and volcanoes (2014)** and the **Circum-Pacific zone (2020)**. Always connect a relief feature to its **plate-tectonic cause and its human use** (minerals on plateaus, farming on alluvial plains) — that linkage earns the marks. ## Further Reading - Standard NCERT-level geography textbooks and reference books, plus a good atlas (any UPSC reading list). ## Test Yourself: Practice Questions & PYQs Test yourself on orogeny, the four mountain types, horst-graben, plateaus and plains. Attempt each before revealing the answer. ## Practice Questions **Q1.** The process of mountain building by the Earth's internal forces is called: - (a) Orogeny - (b) Denudation - (c) Isostasy - (d) Epeirogeny **Answer: (a)** — Orogeny is mountain building (folding/faulting, horizontal forces). Epeirogeny is broad continental uplift/subsidence (vertical). Isostasy is crust-mantle balance; denudation is wearing down by erosion. **Q2.** Which one of the following is a YOUNG fold mountain? - (a) The Appalachians - (b) The Andes - (c) The Urals - (d) The Aravallis **Answer: (b)** — The Andes are young fold mountains at the active South America–Pacific margin (hence earthquakes/volcanoes). The Aravallis, Appalachians and Urals are OLD, worn-down fold mountains. **Q3.** In block-mountain country, the down-dropped block forming a rift-valley floor is called a: - (a) Horst - (b) Nappe - (c) Graben - (d) Monadnock **Answer: (c)** — A graben is the down-faulted block (its floor = rift valley). A horst is the uplifted block (the block mountain). A nappe is an overthrust fold; a monadnock is a residual hill. **Q4.** Mt. Fuji, Mt. Mayon and Mt. Kilimanjaro are examples of which type of mountain? - (a) Fold mountains - (b) Block mountains - (c) Volcanic mountains - (d) Residual mountains **Answer: (c)** — These are volcanic mountains ('mountains of accumulation') built by erupted lava and ash piling around a vent. They are common along the Circum-Pacific belt. **Q5.** The Aravalli Range of India is best described as a: - (a) Block mountain - (b) Residual (old fold) mountain - (c) Volcanic mountain - (d) Young fold mountain **Answer: (b)** — The Aravallis are among the world's oldest fold mountains, now worn down by long denudation into a residual range — not young, block or volcanic. **Q6.** Why are young fold mountains associated with earthquakes and volcanic activity? - (a) They form by vertical faulting away from plate edges - (b) They are made of volcanic rock only - (c) They lie along active converging plate boundaries - (d) They are the oldest mountains on Earth **Answer: (c)** — Young fold mountains form at active converging plate boundaries, where subduction/collision generates the seismicity and volcanism — the link UPSC asked in 2014 (and the Circum-Pacific belt in 2020). **Q7.** The highest and largest plateau in the world, enclosed by mountain ranges, is the: - (a) Deccan Plateau - (b) Tibetan Plateau - (c) Columbia Plateau - (d) Bolivian Plateau **Answer: (b)** — The Tibetan Plateau is the highest and largest intermontane (tectonic) plateau, hemmed in by the Himalayas, Karakoram and Kunlun. The Deccan is a volcanic/lava plateau. **Q8.** The slow rise of the crust after erosion or melting of ice strips weight off it is explained by: - (a) Isostasy - (b) Subduction - (c) Orogeny - (d) Lateral erosion **Answer: (a)** — Isostasy is the buoyant balance between crust and mantle: remove load (erosion, melting ice) and the lightened crust rises (isostatic uplift); add load and it subsides. ### UPSC Previous Year Questions (PYQs) *Two questions UPSC has actually asked on mountain building. Both are matching questions — know which named range belongs to which TYPE, and the classic proofs of continental drift.* **Q9.** Consider the following pairs of mountain ranges and their type: 1. Appalachians — Fold mountains 2. Andes — Fold mountains 3. Ural — Block mountains 4. Sierra Nevada — Residual mountains. How many pairs are correctly matched? (UPSC Prelims 2024) - (a) Only three - (b) Only one - (c) Only two - (d) All four **Answer: (c)** — Only two. The Appalachians and the Andes are both fold mountains — the Appalachians ancient and worn down, the Andes young and still rising at a subduction margin. The Urals are also FOLD mountains, not block, and the Sierra Nevada is a BLOCK mountain formed by faulting, not a residual one. **Q10.** Which of the following are evidences of the phenomenon of continental drift? I. The belt of ancient rocks from the Brazil coast matches with those from Western Africa. II. The gold deposits of Ghana are derived from the Brazil plateau when the two continents lay side by side. III. The Gondwana system of sediments from India has counterparts in six different landmasses of the Southern Hemisphere. (UPSC Prelims 2025) - (a) I and II only - (b) II and III only - (c) I, II and III - (d) I and III only **Answer: (c)** — All three. These are Wegener's classic proofs: the jigsaw fit plus matching 2,000-million-year-old rock belts across the Atlantic, the placer gold of Ghana with no local source rock, and the Gondwana sequence recurring in India, Africa, South America, Antarctica, Australia and the Falklands. ### Mains Practice Questions Use these to frame full-length answers. You don't have to answer one exactly — they show the angles UPSC tests, so let them guide which points you cover. - Why are fold mountains located along continental margins, and how does their distribution relate to earthquakes and volcanoes? (UPSC Mains 2014) - Discuss the geophysical characteristics of the Circum-Pacific zone. (UPSC Mains 2020) - Distinguish between fold, block, volcanic and residual mountains with suitable examples. - Explain horsts, grabens and rift valleys with examples from Africa and India. - Classify plateaus and plains by origin and bring out their economic significance. ### UPSC Mains — Previous Years’ Questions on this topic (last 10 years) These are the **actual GS Mains questions** UPSC has asked on this theme — real proof of how, and when, it is tested. Try to write a full answer to each. - **2014:** Why are the world's fold mountain systems located along the margins of continents? Bring out the association between the global distribution of fold mountains and the earthquakes and volcanoes. - **2020:** Discuss the geophysical characteristics of the Circum-Pacific Zone. - **2014:** Explain the formation of thousands of islands in the Indonesian and Philippine archipelagos.