Lesson 5 – Mountain Formation: Vocabulary Flashcards

A set of vocabulary flashcards summarizing key terms, processes, mountain types, and structural features discussed in Lesson 5 on Mountain Formation.

Mountain

A landform that rises more than 600 m above its surroundings, with steep slopes, a confined summit, and significant local relief.

Orogeny (Mountain-Building)

The suite of geological processes—folding, thrust faulting, compression, metamorphism, and igneous intrusion—that create mountains.

Isostasy

The tendency of Earth’s lighter continental crust to float in gravitational balance on the denser mantle, controlling crustal elevation.

Accumulation Stage

First stage of mountain formation in which 2–3 km of sedimentary and volcanic layers collect in a marine basin or geosyncline.

Orogenic Stage

Phase when intense tectonic stress folds, faults, metamorphoses, and intrudes accumulated rocks, producing the mountain core.

Isostatic Rebound

Upward rise of crust after removal of heavy load (e.g., ice sheet), helping mountains gain additional height.

Folded Mountains

Mountains formed when compressional forces crumple sedimentary layers into folds at convergent plate boundaries (e.g., Himalayas).

Anticline

An upward-arching fold with the oldest rocks at its core; forms ridges.

Syncline

A downward-arching fold (trough) with the youngest rocks at its core.

Monocline

A step-like fold characterized by a single limb of markedly steeper dip within otherwise horizontal strata.

Symmetrical Fold

A fold whose vertical axial plane gives mirror-image limbs on either side.

Asymmetrical Fold

A fold whose axial plane is inclined, so the two limbs dip at different angles.

Recumbent Fold

A fold lying on its side with nearly horizontal axial plane and limbs, produced by extreme compression.

Nappe

A large, detached recumbent fold thrust forward over other rocks, generated by high ductile deformation.

Fault-Block Mountains

Mountains created when crustal blocks are uplifted or down-dropped along normal faults instead of folding.

Horst

An uplifted crustal block bounded by normal faults on both sides.

Graben

A down-dropped crustal block bordered by normal faults, often forming rift valleys.

Dome Mountains (Upwarped Mountains)

Rounded, uplifted mountains produced when rising magma pushes rock layers upward without erupting.

Volcanic Mountains

Mountains built from accumulated lava, ash, and pyroclastics erupted onto Earth’s surface (e.g., Mt. Pinatubo).

Divergent Plate Boundary

A boundary where plates move apart, generating new seafloor, submarine ridges, fissure eruptions, and fractures.

Convergent Plate Boundary

A boundary where plates collide, producing subduction zones, trenches, volcanic arcs, and folded mountain belts.

Transform Plate Boundary

A boundary where plates slide horizontally past one another along faults, causing earthquakes and linear valleys.

Isoclinal Fold

A tight fold whose limbs are parallel to each other due to intense compression.

Basin (Structural)

A bowl-shaped downward fold with beds dipping toward a central point; the opposite of a dome.

Hogback

A narrow, steep-sided ridge formed by erosion of steeply tilted resistant strata.

Upwarped Mountain

Alternate term for dome mountain—rock layers arched upward by intruding magma.

Sierra Nevada

A U.S. example of fault-block mountains uplifted along large normal faults.

Andes Mountains

The world’s longest continental mountain range in South America, formed chiefly by plate convergence and folding.