This page lists 27 geological features that start with R, from “Rift Valley” to “Rubble Mound.” They include landforms, rock types, and water features found on land, along coasts, and even on the Moon and Mars. Studying them helps geologists read Earth’s history, hikers and travelers recognize what they see, and students learn how the planet changes over time.
Geological features are natural formations on a planet’s surface or just beneath it, shaped by forces like tectonic movement, erosion, volcanic activity, and water. The “Ring of Fire,” for example, is a horseshoe-shaped belt around the Pacific Ocean that stretches about 25,000 miles and holds most of the world’s earthquakes and volcanoes.
Below you’ll find the table with the feature, region, characteristics, and description for each one.
Feature: The name of each formation, listed so you can quickly find a term you want to look up or learn about.
Region: Where you can find the feature, from a specific place like East Africa to broad areas like coastlines or mountain ranges.
Characteristics: A short set of key traits, such as shape, rock type, or how it formed, so you can spot differences at a glance.
Description: A plain-language explanation of what the feature is and how it forms, with examples that help you picture it.
Geological features
| Feature | Region | Characteristics |
|---|---|---|
| Rift Valley | East Africa | Tectonic trough, volcanic activity, lakes |
| Rift | Worldwide | Crack in the crust, extensional faulting |
| Ridge | Worldwide | Elongated crest, steep slopes |
| Rock Arch | Western United States, Jordan | Natural opening, eroded sandstone |
| Rock Shelter | Worldwide | Shallow overhang, sheltered hollow |
| Rock Glacier | Alpine and Arctic mountains | Debris-covered ice, slow creep |
| Rockfall | Mountain regions | Loose boulders, steep cliffs |
| Rockslide | Mountain regions | Rapid downslope movement, fractured rock |
| Rhyolite | Yellowstone, Iceland, New Zealand | Silica-rich volcanic rock, light colored |
| Roche Moutonnée | Glaciated regions, Scotland, Scandinavia | Smooth up-ice side, jagged down-ice side |
| Ria | Galicia (Spain), southwest Ireland, Brittany | Drowned river valley, branching inlet |
| Ring of Fire | Pacific Ocean rim | Volcanoes, earthquakes, subduction zones |
| Ring Dike | Worldwide | Circular intrusion, igneous rock |
| Rille | Moon, Mars | Narrow channel, sinuous or straight |
| Rock Pinnacle | Worldwide | Tall spire, resistant rock |
| Rock Pool | Rocky coastlines | Tidal basin, marine habitat |
| Rock Terrace | Worldwide | Flat step, resistant layers |
| Rapids | Rivers worldwide | Fast-flowing water, steep gradient |
| Rift Lake | East Africa, Siberia, Dead Sea region | Deep basin, fault-bounded |
| Ravine | Worldwide | Narrow, steep-sided, stream-cut |
| Reef | Tropical coasts, Great Barrier Reef | Ridge of coral or rock, shallow water |
| Regolith | Worldwide, Moon | Loose surface layer, weathered fragments |
| Rock Salt Dome | Gulf Coast (USA), Iran, Germany | Rising salt column, dome-shaped uplift |
| Red Beds | Southwestern United States, England | Iron-stained sedimentary layers, red color |
| Rimrock | Western United States | Resistant cap rock, cliff edge |
| Rock Spring | Worldwide | Groundwater outflow, rock fissure |
| Rubble Mound | Mountain and coastal areas | Loose broken rock, irregular heap |
Descriptions
Rift Valley
A long valley formed where tectonic plates pull apart. The East African Rift stretches for thousands of miles and is slowly splitting the continent.
Rift
A zone where the Earth’s crust is stretched and thinned, creating a sunken valley bordered by faults. Rifts can eventually grow into new ocean basins.
Ridge
A long, narrow elevated landform with a crest running along its length. Ridges form through folding, faulting, erosion, or volcanic activity.
Rock Arch
A natural opening in a rock formation carved out by weathering and erosion. Arches National Park in Utah has more than 2,000 of them.
Rock Shelter
A shallow cave-like space under a cliff overhang formed by erosion. Early humans often used these shelters, and many hold ancient rock art.
Rock Glacier
A tongue of loose rock and ice that slowly creeps downslope. It looks like a rubble stream but moves like a very slow glacier.
Rockfall
The sudden falling of rock fragments from a steep cliff or slope. It is common where freeze-thaw cycles and gravity loosen the rock.
Rockslide
A fast movement of large masses of rock sliding down a slope along a fracture or bedding plane. Rockslides can dam rivers and bury valleys.
Rhyolite
A pale, fine-grained volcanic rock rich in silica. It forms from thick, sticky lava and is linked to explosive eruptions.
Roche Moutonnée
A bedrock knob shaped by a glacier moving over it. The side facing the ice is polished smooth, while the far side is plucked rough.
Ria
A coastal inlet formed when rising seas flood a river valley. Rias tend to be long, branching, and gradually deepening toward the sea.
Ring of Fire
A horseshoe-shaped belt around the Pacific where most of the world’s earthquakes and volcanic eruptions occur. It stretches about 25,000 miles.
Ring Dike
A circular or arc-shaped body of igneous rock that cuts through older rock. It forms when magma rises along a ring-shaped fracture around a collapsed volcanic center.
Rille
A long, narrow trench-like valley on the surface of a planetary body. Lunar rilles are thought to be collapsed lava tubes or ancient lava channels.
Rock Pinnacle
A tall, slender rock spire left standing after the surrounding rock has eroded away. Pinnacles often form in arid regions or along coasts.
Rock Pool
A shallow depression in coastal rock that holds seawater when the tide goes out. These pools host small marine life like crabs, anemones, and snails.
Rock Terrace
A flat, step-like bench in a hillside or river valley. Terraces form where layers of rock erode at different rates or where a river cut down into its former floodplain.
Rapids
A stretch of a river where water flows quickly over a steep, rocky bed. Rapids form where the riverbed drops or contains hard, resistant rock.
Rift Lake
A lake that fills a basin created by rifting of the crust. Lake Tanganyika and Lake Baikal are among the deepest lakes in the world.
Ravine
A small, narrow valley with steep sides, usually carved by running water. It is larger than a gully but smaller than a canyon.
Reef
A ridge of rock, sand, or coral lying just below the water’s surface. Coral reefs are built by living organisms over thousands of years.
Regolith
The blanket of loose dust, soil, and broken rock covering solid bedrock. It exists on Earth and also covers the Moon’s surface.
Rock Salt Dome
A mound of salt that has pushed upward through denser rock layers. These domes often trap oil and gas around their edges.
Red Beds
Sedimentary rock layers colored red by iron oxide. They often point to arid or oxygen-rich environments when the sediments were deposited.
Rimrock
A layer of hard rock forming the edge of a plateau or cliff. It caps softer rock beneath and creates steep escarpments.
Rock Spring
A spring where groundwater flows out through cracks or openings in bedrock. It often marks the point where an aquifer meets the surface.
Rubble Mound
A heap of angular broken rock fragments piled up by landslides or frost shattering. Similar rubble heaps are also called talus or scree.