What moves weathered material across Earth's surface, and how can we tell which agent did it?
Identify the agents of erosion (running water, glaciers, wind, waves and gravity) and use the characteristic shapes and deposits of sediment to infer which agent transported it.
A Regents answer on erosion: the agents that transport sediment (running water, glaciers, wind, waves, gravity), why running water is the dominant agent, the tell-tale evidence each agent leaves (rounded versus angular particles, scratched and grooved bedrock, V-shaped versus U-shaped valleys, sorted versus unsorted deposits), with worked exam questions.
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What this topic is asking
The Regents wants you to name the agents of erosion and to infer which agent transported a sediment from the evidence it leaves: the shape of particles, the marks on bedrock, the shape of valleys, and whether deposits are sorted or unsorted. Erosion is the transport step, separate from weathering (breakdown) and deposition (dropping).
The agents of erosion
Running water carries the most sediment overall and shapes most landscapes. Faster, more turbulent water carries more and larger particles (the next topic covers the particle-size graph). Gravity acts on its own in landslides and rockfalls and also pulls water and ice downhill, so it underlies the other agents.
The evidence each agent leaves
Reading particle shape
Glacial evidence in New York
New York's landscape is full of glacial evidence from the last ice age: striated and grooved bedrock, U-shaped valleys (such as the Finger Lakes basins), unsorted till, erratic boulders carried far from their source, and moraines (ridges of dumped till). This is direct evidence that glaciers once covered the state.
Try this
Q1. State the dominant agent of erosion on Earth's land surface. [1 point]
- Cue. Running water (streams and rivers).
Q2. Explain how you can tell glacial deposits from stream deposits. [2 points]
- Cue. Glacial deposits (till) are unsorted, with mixed sizes dropped together; stream deposits are sorted and rounded, separated by size as the water slows.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart A. A region shows U-shaped valleys, scratched and grooved bedrock, and large unsorted deposits of mixed boulders, sand and clay. The agent of erosion most likely responsible is (1) wind (2) running water (3) a glacier (4) ocean waves. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (3).
U-shaped valleys, scratched (striated) and grooved bedrock, and unsorted deposits of mixed sizes (till) are the signature of glacial erosion and deposition. Running water (2) carves V-shaped valleys and leaves sorted, rounded sediment; wind (1) moves only fine particles and leaves frosted, well-rounded sand; waves (4) work along shorelines. The trap is choosing running water; the unsorted, mixed-size deposit and the U-shape point to ice.
Regents (style)2 marksPart B-2. A student examines pebbles from a streambed and finds they are smooth and well rounded, while pebbles from a nearby cliff base are sharp and angular. (a) Explain what the rounding of the streambed pebbles indicates about their history. (b) Identify the agent that rounded them and the process involved.Show worked answer →
A 2-point constructed-response question.
(a) 1 point: the rounded pebbles have been transported a long way; the more rounded a particle, the longer or farther it has been carried.
(b) 1 point: running water (a stream) transported them, and abrasion (the particles rubbing and knocking against one another and the bed) wore off their sharp edges, rounding them.
Markers reward linking rounding to transport distance/time, and naming running water plus abrasion. The angular cliff-base pebbles, by contrast, have barely moved.
Related dot points
- Distinguish physical from chemical weathering, explain the factors that control the rate of weathering (climate, surface area, rock type), and describe how weathering and other processes form soil.
A Regents answer on weathering and soil: physical (mechanical) weathering such as frost wedging versus chemical weathering such as carbonation and oxidation, how climate, surface area and rock type control the rate, why warm wet climates weather chemically faster, and how soil forms as a mix of weathered rock and organic matter, with worked exam questions.
- Explain how deposition occurs as transporting agents lose energy, and use the Reference Tables relationship of particle size to water velocity, together with particle size, shape and density, to predict settling order and sorting.
A Regents answer on deposition and sorting: how sediment is dropped when a transporting agent slows, the Reference Tables graph of transported particle size versus water velocity, why larger and denser particles settle first, horizontal and vertical sorting, graded bedding, and how rounded versus angular shape affects settling, with worked exam questions.
- Describe stream behavior and drainage patterns, and use topographic (contour) maps with the Reference Tables gradient equation to calculate gradient, determine stream flow direction and read elevations.
A Regents answer on streams and topographic maps: how stream velocity changes with gradient and discharge, the inside versus outside of meanders, reading contour lines, the rule that contour lines bend upstream (V points uphill), determining flow direction, and using the Reference Tables gradient equation, with worked exam questions and a full gradient calculation.
- Explain how landscapes are classified (mountains, plateaus, plains) by elevation, relief and structure, how climate and bedrock control landscape development, and use the Reference Tables map of New York's landscape regions.
A Regents answer on landscapes: how mountains, plateaus and plains are classified by elevation, relief and rock structure, how climate (arid versus humid) and bedrock resistance shape landscape development, stream drainage patterns, and how to use the Reference Tables Generalized Landscape Regions and Bedrock Geology maps of New York, with worked exam questions.
- Use the Reference Tables Geologic History of New York State and the bedrock map to read New York's tectonic and environmental history, including ancient mountain-building, shallow seas and the most recent glaciation.
A Regents answer on New York's geologic history: how to read the Geologic History of New York State chart and the bedrock map together, the ancient mountain-building (orogenies), the shallow seas that left marine fossils and sedimentary rock, the oldest Precambrian rock of the Adirondacks, and the last ice age that shaped today's landscape, with worked exam questions.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)