Short answer
Weathering breaks down or chemically changes rock where it is. Erosion removes and transports material. If ice widens a crack in a rock, that is physical weathering. If runoff carries away the loosened fragments, that is erosion. The processes often work together, but they describe different parts of the change. 1 2
This distinction is most useful when applied to a specific process. A changing cliff or stream channel can show weathering, erosion, and deposition at once; it does not need one label for everything happening there. 3
On this page
At a glance
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| Question | Weathering | Erosion |
|---|---|---|
| Main action | Breaks rock into smaller pieces or alters its minerals. | Removes and moves material. |
| Does transport define it? | No; alteration or breakdown occurs in place. | Yes, in the distinction used here. |
| Typical agents | Water, chemical reactions, temperature changes, ice growth, and roots. | Moving water, wind, and glacier ice. |
| Must the chemistry change? | No; physical weathering leaves the minerals’ chemistry unchanged. | No; transport itself does not require a chemical change. |
| Illustrative example | Rock cracks as ice grows in it. | A stream carries fragments downstream. |
| Related next step | May make material easier to remove. | Material may later be deposited elsewhere. |
Definitions and agents: 1 2. Connections with deposition: 3.
What each thing is
Weathering
Physical weathering breaks rock without changing the chemical makeup of its individual minerals. Water freezing in cracks and repeated expansion and contraction with temperature are examples. Roots can also widen existing openings. 1
Chemical weathering changes minerals through chemical processes. Dissolution is one example: water, often containing weak acid, dissolves components of rock. Weathering therefore does not always leave a pile of visible pebbles or sand. Some products enter solution. 1
Erosion
In the usage followed here, erosion involves moving material away. Streams can carry sediment, wind can move loose particles, and glaciers can transport rock and reshape a landscape. The agent matters for explaining how movement happens, but movement is the key distinction from weathering in place. 2
Deposition is the accumulation of material after transport. A stream can erode one part of its channel and deposit sediment in another. Calling the entire sequence “erosion” can hide this final step. 2 3
Key differences
The same agent can do different jobs
Water can cause weathering by helping minerals dissolve or by freezing in cracks. Moving water can then erode the material it carries away. “Water caused it” is therefore not enough to select the term; the relevant question is what the water did. 1 3
Smaller pieces and movement are separate observations
A rock that has fractured but remains in place has changed without its fragments necessarily being carried away. Sediment moving downstream may already have been loose before the current flow began. The distinctions describe actions, rather than a rule that every episode of transport must begin with a freshly broken rock. 1 2
Chemical weathering complicates the visual shortcut
The rule “weathering makes pieces; erosion moves pieces” works for many physical examples but leaves out dissolved material. NPS describes dissolution as a chemical weathering process even though the dissolved products can be carried away by water. Separate the chemical reaction at the rock surface from the subsequent transport when that detail matters. 1
How to tell them apart
Ask three questions about the process being described:
- Did rock fracture or its minerals change at that location? That is evidence of weathering.
- Was material removed and transported? That is evidence of erosion.
- Did transported material accumulate? That is deposition.
These are questions about events. A single photograph may show a cracked boulder or a sediment pile without revealing exactly how it formed. Context, repeated observations, or geological interpretation may be needed to connect the visible feature to the process. 1 2 3
Where they overlap
Weathering can supply material for erosion, while erosion exposes new surfaces to weathering. At Scotts Bluff National Monument, NPS describes rock breakdown by processes including ice and salt crystal growth, followed by removal of particles by wind and water. The landscape reflects their combined effects. 3
Edge cases
Dissolving rock: no visible fragment needs to detach for chemical weathering to occur. Dissolved material may subsequently travel with water. 1
One river, several processes: a channel may lose sediment along one bank while building a sandbar elsewhere. The erosion/deposition distinction depends on the location and action being considered. 3
Glacier ice versus ice in a crack: ice growth can break rock in place; a moving glacier can transport rock. The presence of ice alone does not identify the process. 1 2
Why the distinction exists
The terms separate breakdown, movement, and accumulation. That helps explain why one surface is weakening, why another is losing material, and why sediment is collecting elsewhere. Describing the steps separately gives a more useful account than saying only that the landscape is wearing away. 1 2 3
Common misconceptions
Examples
Consider an illustrative sequence: ice opens a crack; a fragment breaks free; runoff carries smaller material downslope; a stream deposits it in a bar. The first breakdown is weathering, transport is erosion, and accumulation is deposition. Real sites may repeat or combine these steps. 1 3
Sources
Sources consulted October 3, 2026.
- National Park Service — Weathering. Physical weathering, chemical weathering, and dissolution.
- National Park Service — Erosion. Transport by water, wind, and glacier ice; sediment deposition.
- National Park Service — Weathering and Erosion, Scotts Bluff. Local examples and changes in stream channels.