This page lists 45 geological features that start with S, from “Sand Dune” to “Sinter Terrace.” They include rocks, landforms, coastal shapes, volcanoes, faults and water features found on land and under the sea. People use this knowledge to study Earth’s history, find oil and water, build with stone, and plan safe travel.
Geological features are the natural shapes, rocks and structures that form the surface and interior of the Earth. Some are famous worldwide, like the white terraces of Pamukkale in Turkey or the slot canyons of the American Southwest.
Below you’ll find the table with the geological feature, its region, its characteristics and a short description.
Geological Feature: The name of each feature, listed alphabetically, so you can quickly find the one you want or browse the full list from start to finish.
Region: The places where each feature is commonly found, which helps you spot where in the world to see it or learn about it.
Characteristics: A short summary of the key traits of each feature, so you can understand what it is and tell similar ones apart at a glance.
Description: A clear explanation of how each feature forms and why it matters, often with a well-known example that you can look up.
Geological features
| Geological Feature | Region | Characteristics |
|---|---|---|
| Sand Dune | Deserts and coasts worldwide | Wind-blown ridge of sand |
| Sandbar | Coasts and rivers worldwide | Underwater or exposed sand ridge |
| Sandstone | Worldwide | Sedimentary rock made of sand grains |
| Scarp | Worldwide | Steep slope or cliff face |
| Sea Arch | Coastlines worldwide | Natural rock bridge cut by waves |
| Sea Cave | Rocky coastlines worldwide | Hollow carved by waves |
| Sea Cliff | Coastlines worldwide | Steep rock face meeting the sea |
| Sea Stack | Coastlines worldwide | Isolated rock column in the sea |
| Seamount | Ocean basins worldwide | Underwater volcanic mountain |
| Sediment | Worldwide | Loose particles deposited by water, wind or ice |
| Sedimentary Basin | Worldwide | Large depression filled with sediment |
| Seismic Fault | Plate boundaries worldwide | Fracture where rock blocks move |
| Shale | Worldwide | Fine-grained layered sedimentary rock |
| Shield Volcano | Hawaii, Iceland, Galapagos | Broad, gently sloping cone |
| Sill | Worldwide | Flat sheet of igneous rock |
| Sinkhole | Florida, Mexico, China, Slovenia | Ground collapse into a cavity |
| Slot Canyon | American Southwest, Namibia, Australia | Deep, extremely narrow canyon |
| Spit | Coastlines worldwide | Sand or gravel strip extending into water |
| Spring | Worldwide | Natural groundwater outlet |
| Stalactite | Limestone caves worldwide | Mineral formation hanging from a cave ceiling |
| Stalagmite | Limestone caves worldwide | Mineral formation rising from a cave floor |
| Stratovolcano | Pacific Ring of Fire, Italy, Indonesia | Steep cone of layered lava and ash |
| Strike-Slip Fault | California, New Zealand, Turkey | Sideways-moving fracture |
| Subduction Zone | Pacific Ring of Fire, Mediterranean, Caribbean | Plate sinking beneath another |
| Syncline | Mountain belts worldwide | Downward fold in rock layers |
| Salt Dome | Gulf of Mexico, Germany, Iran | Rising column of salt |
| Salt Flat | Bolivia, Utah, Chile, India | Flat expanse of salt crust |
| Salt Lake | Utah, Israel and Jordan, Australia | Lake with high salt content |
| Scoria Cone | Volcanic fields worldwide | Small cone of volcanic cinders |
| Sea Mount Chain | Pacific Ocean | Line of underwater volcanoes |
| Seafloor Spreading Ridge | Mid-Atlantic, East Pacific | Underwater crack where new crust forms |
| Silt | Floodplains and river deltas worldwide | Fine sediment particles |
| Slate | Wales, Vermont, Spain | Fine-grained metamorphic rock |
| Soil | Worldwide | Weathered rock mixed with organic matter |
| Strait | Worldwide | Narrow waterway between landmasses |
| Stream Terrace | River valleys worldwide | Step-like old floodplain |
| Syenite | Norway, Brazil, Canada | Coarse igneous rock |
| Schist | Scotland, New York, Alps | Shiny, flaky metamorphic rock |
| Serpentine Barrens | Pennsylvania, California, Cuba | Thin, mineral-rich soil from serpentinite |
| Solfatara | Italy, Iceland, Japan | Volcanic vent releasing sulfur gases |
| Strata | Worldwide | Layers of sedimentary rock |
| Sulfur Spring | Yellowstone, Iceland, Japan | Water carrying sulfur compounds |
| Sunda Trench | Indian Ocean, Indonesia | Deep subduction trench |
| Scree | Mountain slopes worldwide | Broken rock debris at a slope base |
| Sinter Terrace | Yellowstone, New Zealand, Turkey | Mineral deposit around hot springs |
Descriptions
Sand Dune
A hill or ridge of loose sand shaped by the wind. Dunes slowly migrate downwind and come in forms such as crescent, linear and star shapes.
Sandbar
A ridge of sand built up by waves or river currents near a shore or in a channel. Sandbars often shift with storms and tides.
Sandstone
A sedimentary rock formed from compacted and cemented sand grains. It is used widely as a building stone and forms cliffs, arches and canyons.
Scarp
A steep slope that marks the edge of a plateau or the line of a fault. Scarps form through faulting or erosion.
Sea Arch
An opening carved through a headland by wave action. Over time the arch can collapse and leave a sea stack behind.
Sea Cave
A cavity eroded into a sea cliff by the constant pounding of waves. Sea caves form along weaknesses such as joints and faults.
Sea Cliff
A steep rock face along a coast, cut back by wave erosion. Famous examples include the White Cliffs of Dover.
Sea Stack
A tall, narrow column of rock standing just off a coast. It is left behind when waves erode the surrounding headland.
Seamount
An underwater mountain that rises from the seafloor without reaching the surface. Most are extinct volcanoes and attract rich marine life.
Sediment
Loose material such as sand, silt and clay that is carried and dropped by water, wind or ice. Layers of sediment eventually harden into sedimentary rock.
Sedimentary Basin
A broad sunken area of the crust where thick layers of sediment pile up over millions of years. Many oil and gas fields are found in them.
Seismic Fault
A fracture in the crust along which rocks have moved. Sudden slip on a fault causes earthquakes.
Shale
A soft sedimentary rock made of compacted mud and clay that splits into thin layers. Some shales hold oil and natural gas.
Shield Volcano
A wide volcano built from fluid lava flows that spread far before cooling. Mauna Loa in Hawaii is a classic example.
Sill
A sheet of magma that squeezed between existing rock layers and hardened. Sills run parallel to the layers they intrude.
Sinkhole
A depression or hole that opens when the ground above a dissolved or hollow underground space gives way. Sinkholes are common in limestone regions.
Slot Canyon
A canyon much deeper than it is wide, carved by flash floods through soft rock such as sandstone. Antelope Canyon in Arizona is a famous one.
Spit
A narrow strip of sand or shingle that juts out from the shore, built by longshore drift. Cape Cod’s hook is a well-known spit.
Spring
A place where groundwater flows naturally to the surface. Springs can be cold or hot and often feed streams and rivers.
Stalactite
An icicle-shaped deposit that grows downward from a cave roof as mineral-rich water drips. It grows very slowly, often a few millimeters per century.
Stalagmite
A mound or spike of minerals that builds up from the cave floor where dripping water lands. It can eventually meet a stalactite to form a column.
Stratovolcano
A tall, steep volcano made of alternating layers of lava, ash and rock. Mount Fuji and Mount St. Helens are examples.
Strike-Slip Fault
A fault where two blocks of crust slide horizontally past each other. The San Andreas Fault is a famous example.
Subduction Zone
A boundary where one tectonic plate dives beneath another into the mantle. These zones produce deep trenches, volcanoes and powerful earthquakes.
Syncline
A trough-shaped fold in which rock layers bend downward, with the youngest rocks at the center. It is the opposite of an anticline.
Salt Dome
A mound formed when buried salt layers push upward through heavier rock. Salt domes often trap oil and gas.
Salt Flat
A flat area covered in salt left behind after a lake or sea water evaporates. The Salar de Uyuni in Bolivia is the largest in the world.
Salt Lake
A lake with a salinity much higher than a typical freshwater lake. The Dead Sea and Great Salt Lake are well-known examples.
Scoria Cone
A steep little volcano built from fragments of frothy lava that fall around a vent. It is also called a cinder cone.
Sea Mount Chain
A string of seamounts formed as a plate moves over a hot spot. The Hawaiian-Emperor chain is a classic example.
Seafloor Spreading Ridge
A place on the ocean floor where plates pull apart and magma rises to create new crust. The Mid-Atlantic Ridge is the best-known example.
Silt
A very fine sediment, coarser than clay but finer than sand. Silt makes river floodplains fertile.
Slate
A smooth rock formed when shale is squeezed and heated. It splits into flat sheets and has long been used for roofing.
Soil
The loose top layer of the Earth’s surface made of broken rock, air, water and decayed life. It supports plants and forms over hundreds to thousands of years.
Strait
A narrow channel of water linking two larger bodies of water. Many straits were formed by sea-level rise or tectonic movement.
Stream Terrace
A flat, step-shaped surface left above a river after the stream cuts down into its valley. Terraces record past river levels.
Syenite
A light-colored igneous rock similar to granite but with little or no quartz. It forms deep underground from cooling magma.
Schist
A metamorphic rock with visible, sparkly mica flakes that align in layers. It forms under high heat and pressure deep in the crust.
Serpentine Barrens
Areas where serpentinite rock produces poor soil with heavy metals, supporting unusual plant communities.
Solfatara
A volcanic area where hot sulfurous gases seep from the ground without erupting. The Solfatara crater near Naples is the best-known example.
Strata
The distinct layers of rock stacked on top of each other, each representing a period of deposition. Strata let geologists read Earth’s history.
Sulfur Spring
A spring whose water contains dissolved sulfur, giving off a rotten-egg smell. Many sulfur springs are warm and used as spas.
Sunda Trench
A deep ocean trench off the coast of Sumatra and Java where the Indo-Australian Plate sinks beneath the Sunda Plate. It was the source of the 2004 Indian Ocean tsunami.
Scree
A sloping pile of loose rock fragments that fall from cliffs and gather below. Scree slopes are loose and hard to climb.
Sinter Terrace
A stepped formation of silica or other minerals left behind by hot spring water. Pamukkale in Turkey has famous white terraces.