This page lists 31 geological features that start with I, running from “Ice cap” to “Itatiaia massif.” The list covers frozen landforms, volcanic and rock features, water and land shapes, and famous places. It helps students, travelers, hikers, and curious readers learn the names and compare features quickly.
Geological features are the natural shapes and structures that make up Earth’s surface and interior, formed by ice, water, wind, volcanoes, and moving plates. Some are surprisingly dramatic, like the Khumbu Icefall on Mount Everest, which climbers cross each spring on their way to the summit.
Below you’ll find the table with the feature, region, characteristics, and description for each entry.
Feature: The name of each geological feature, listed alphabetically so you can scan the list and find the one you want.
Region: Where in the world you can find the feature, from whole continents to a single country, lake, or mountain range.
Characteristics: A short summary of what defines the feature, such as its size, shape, or how it formed, so you can compare entries at a glance.
Description: A plain-language explanation of what the feature is, how it works, and a well-known example you can look up or visit.
Geological features
| Feature | Region | Characteristics |
|---|---|---|
| Ice cap | Polar and high-altitude regions worldwide | Dome-shaped glacier, under 50,000 square kilometers |
| Ice sheet | Antarctica and Greenland | Continental scale, over 50,000 square kilometers |
| Ice field | Mountain ranges such as Alaska and Patagonia | Interconnected glaciers, peaks poking through |
| Ice shelf | Antarctica, Greenland, Arctic Canada | Floating, attached to land |
| Ice stream | Antarctica and Greenland | Fast-flowing channel within an ice sheet |
| Iceberg | Polar and subpolar oceans | Floating chunk of freshwater ice, mostly underwater |
| Icefall | Glaciated mountains such as the Himalayas and Alps | Steep, crevassed section of a glacier |
| Ice wedge | Arctic and subarctic permafrost zones | Vertical, V-shaped ice body in frozen ground |
| Ice cave | Glaciers in Iceland, Alaska, Austria and elsewhere | Hollow chamber in or under a glacier |
| Ice dam | Glacial valleys and rivers | Natural barrier of ice blocking water flow |
| Ice-dammed lake | Glaciated regions such as Montana and Iceland | Temporary lake held back by ice |
| Ice age valley | Northern Europe and North America | U-shaped, carved by glaciers |
| Igneous intrusion | Worldwide, including the Scottish Highlands and Sierra Nevada | Magma cooled underground |
| Ignimbrite | Volcanic regions such as the Andes, New Zealand and Yellowstone | Welded volcanic ash deposit |
| Impact crater | Worldwide, including Arizona and Mexico’s Yucatán | Bowl-shaped, caused by a meteorite |
| Inselberg | Africa, Australia and South America | Isolated rocky hill rising from a plain |
| Island arc | Western Pacific, Caribbean, Aleutians | Curved chain of volcanic islands |
| Isthmus | Panama, Suez, Corinth | Narrow land bridge between two larger landmasses |
| Island | Every ocean and many lakes and rivers | Land completely surrounded by water |
| Inlet | Coastlines worldwide | Narrow water passage into the land |
| Inner core | Center of the Earth | Solid iron-nickel ball, about 760 miles in radius |
| Interdune | Deserts such as the Sahara and Namib | Flat or low area between dunes |
| Intermontane basin | Western North America, the Andes, Tibet | Low area between mountain ranges |
| Inverted relief | Deserts and old river systems | Former valleys that now stand as ridges |
| Iguazu Falls | Argentina and Brazil border | About 275 waterfalls over a basalt cliff |
| Ijen crater | East Java, Indonesia | Acidic turquoise crater lake, sulfur deposits |
| Iceland hotspot | Iceland | Mantle plume under the Mid-Atlantic Ridge |
| Imja Glacier | Everest region, Nepal | Retreating glacier with a growing lake |
| Ischigualasto | San Juan Province, Argentina | Eroded badlands with fossil-rich rock |
| Isle Royale | Lake Superior, Michigan, USA | Ancient lava and rift rocks |
| Itatiaia massif | Southeastern Brazil | Alkaline rock mountain range |
Descriptions
Ice cap
A dome of ice that covers a highland area, smaller than an ice sheet. Examples include Vatnajökull in Iceland. Ice flows outward from the center toward the edges.
Ice sheet
A huge mass of glacial ice covering land, thousands of feet thick. Only two exist today, in Antarctica and Greenland. They hold most of the freshwater ice on Earth.
Ice field
A large area of mountain ice where several glaciers join together. Mountain peaks, called nunataks, often rise through the ice. The Southern Patagonian Ice Field is a well-known example.
Ice shelf
A thick platform of ice that floats on the sea while still attached to land. Ice shelves slow the flow of glaciers behind them. Large pieces can break off to form tabular icebergs.
Ice stream
A fast-moving river of ice inside a slower ice sheet. Ice streams drain much of the ice from continents into the ocean. Pine Island Glacier is one example.
Iceberg
A large piece of ice that has broken off a glacier or ice shelf and floats in open water. About 90 percent of its volume sits below the surface.
Icefall
A very steep part of a glacier where the ice breaks into a jumble of cracks and towers. The Khumbu Icefall on Mount Everest is among the most famous and dangerous.
Ice wedge
A wedge of ice that grows downward in frozen soil as cracks fill with meltwater and refreeze year after year. Ice wedges shape patterned ground in the tundra.
Ice cave
A cavity inside or beneath glacial ice, often carved by meltwater. Many glow blue from light passing through the ice. They change from year to year and can be unstable.
Ice dam
A blockage of ice that holds back a river or meltwater, forming a lake behind it. When an ice dam breaks, it can release a catastrophic flood.
Ice-dammed lake
A lake that forms when glacier ice blocks a valley. Some drain suddenly in floods. Glacial Lake Missoula was a huge prehistoric example.
Ice age valley
A broad valley with steep sides and a flat floor, carved by glaciers during an ice age. Yosemite Valley is a well-known example.
Igneous intrusion
A body of molten rock that pushed into existing rock and hardened below the surface. Granite batholiths and sills are common types. They are often exposed after erosion removes the rock above.
Ignimbrite
A rock formed from the hardened deposits of a fast-moving cloud of hot ash and gas from a volcanic eruption. Some ignimbrite sheets cover thousands of square miles.
Impact crater
A circular depression made when an asteroid or comet strikes the ground. Meteor Crater in Arizona is one of the best preserved. Chicxulub in Mexico is linked to the dinosaur extinction.
Inselberg
A lone, steep-sided hill or small mountain that stands above a flat landscape after surrounding rock has worn away. Uluru in Australia is a famous example.
Island arc
A curved line of volcanic islands formed where one tectonic plate sinks under another. Japan, the Aleutians and the Lesser Antilles are island arcs.
Isthmus
A thin strip of land with water on both sides that connects two bigger areas of land. The Isthmus of Panama joins North and South America.
Island
A piece of land smaller than a continent that is surrounded by water. Islands form through volcanic activity, coral growth, sediment build-up or rising sea levels.
Inlet
A small arm of the sea or a lake that reaches into the land, or a channel between islands. Inlets can be shaped by glaciers, rivers or drowned valleys.
Inner core
The solid center of the planet, surrounded by liquid outer core. It is extremely hot, around the temperature of the sun’s surface, but pressure keeps it solid.
Interdune
The low area between two sand dunes. Some are bare, damp or hold small ponds, and they preserve useful clues about past wind and water conditions.
Intermontane basin
A broad basin sitting between mountain ranges, often filled with sediment washed down from the slopes. The Great Basin and the Altiplano are examples.
Inverted relief
A landscape where old low features, such as stream beds, become ridges because their hard fill resists erosion better than the surrounding rock. These are seen on Earth and Mars.
Iguazu Falls
One of the largest waterfall systems in the world, spread across a wide curved cliff in the rainforest. The water plunges into a deep gorge called the Devil’s Throat.
Ijen crater
A volcanic crater famous for its bright blue-green acidic lake and its glowing blue flames from burning sulfur gas at night. Workers still mine sulfur here by hand.
Iceland hotspot
A zone of rising hot rock under Iceland that combines with the Mid-Atlantic Ridge to produce frequent volcanic eruptions. It built the island itself and keeps it geologically very active.
Imja Glacier
A Himalayan glacier whose meltwater has built up Imja Lake, a fast-growing glacial lake. The lake has raised concerns about outburst flooding in valleys below.
Ischigualasto
A desert valley, also called the Valley of the Moon, where wind and water have carved odd-shaped rock formations. Its layers hold some of the oldest known dinosaur fossils.
Isle Royale
A remote island made of ancient volcanic and sedimentary rock from the Midcontinent Rift. Glaciers later shaped its ridges and valleys, and it holds native copper deposits.
Itatiaia massif
A mountain range in Brazil formed from alkaline igneous rock. Its high plateau has sharp peaks, cliffs and unusual rock features, including the Agulhas Negras peak.