A mountain valley has a broad, U-shaped cross profile, and its granite walls are polished smooth with long, parallel scratches all running the same direction. Which agent carved it?

A narrow, steep-walled valley shaped like the letter V winds through the hills, with a channel that bends back and forth across its floor. Which agent shaped this valley?

A desert plain is covered in tall, crescent-shaped ridges of sand that slowly shift position over months. Which agent formed these ridges?

At the base of a rocky coastal cliff, the rock is undercut into a notch right at the waterline, with the cliff face above overhanging it. Which agent cut this notch?

A hillside shows a curved, bowl-shaped scar near the top and a jumbled pile of broken soil and rock lower down the slope. Which agent produced this feature?

At the head of a mountain valley, a steep, bowl-shaped hollow is carved into the rock, with a small lake now sitting in its floor. Which agent carved this hollow?

A crescent-shaped lake sits isolated on a flat floodplain, filling an old meander loop that was cut off and abandoned. Which agent formed this lake?

In a desert, an isolated rock stands with a narrow, pitted base and a wider, smoother top, shaped almost like a mushroom. Which agent shaped this rock?

Along a rocky headland, an archway has been cut through a point of land, and a separate pillar of rock stands just offshore from it. Which agent formed these features?

On a grassy hillside, the ground surface has bent trees and small step-like ridges called terracettes running across the slope. Which agent produced these features?

A deposit contains angular boulders, sand, and clay all jumbled together with no layering, and some of the embedded cobbles are scratched with parallel grooves. Which agent deposited this material?

A sediment sample from a dry inland basin is made of well-rounded, well-sorted quartz grains about 0.2 mm across, with frosted, pitted surfaces. Which agent deposited this sediment?

A pile of angular, unsorted rock fragments of many sizes has built up in a steep cone shape at the base of a cliff. Which agent deposited this material?

Along a valley floor, gravel and rounded cobbles sit near the mountains while progressively finer sand and silt appear farther downslope. Which agent deposited this pattern?

A single house-sized granite boulder sits alone on a flat limestone plain in Ohio, hundreds of kilometers from any granite bedrock. Which agent most likely deposited this boulder?

A beach sample is made of well-rounded, well-sorted sand grains mixed with broken shell fragments, arranged in thin, even bands. Which agent deposited this sediment?

A thick, unstratified blanket of fine silt covers hundreds of square kilometers far from any mountains or rivers. Which agent deposited this silt?

In a gravel deposit on a dry valley floor, rounded, flat cobbles all lie overlapping and tilted in the same direction, like tiles on a roof. Which agent deposited them?

Two erosion agents are compared for the largest particle each can transport. Which agent, shown in Panel B, can move boulders together with sand and clay in one unsorted mass?

Two erosion agents are compared by the grain size each carries. Which agent is shown in Panel A?

Two erosion agents are compared by how fast they move material. Which agent is shown moving material fastest, in Panel B?

Two erosion agents are compared by what they can dissolve and carry. Which agent, shown in Panel B, can carry part of its load as dissolved minerals a person cannot see?

Two erosion agents are compared for how long they take to reshape a landscape. Which agent, shown in Panel B, reshapes landscapes over the longest span of time?

Two erosion agents are compared for what they can move instantly. Which agent, shown in Panel A, is capable of moving a boulder instantly?

Two erosion agents are compared by how they sort sediment along a coast. Which agent, shown in Panel B, sorts sediment through repeated motion up and down a beach?

A stream in flood carries sand bouncing along the streambed in short hops while gravel rolls and slides beside it. What is the bouncing motion of the sand called?

In the same flooded stream, gravel and pebbles too heavy to lift are pushed and rolled along the bottom without ever leaving it. What is this transport mechanism called?

Clay and silt particles stay mixed throughout a river's water and give it a muddy color, even where the current briefly slows. What is this transport mechanism called?

A stream flowing over limestone bedrock carries calcium ions dissolved in the water, invisible to the eye. What is this transport mechanism called?

In a sandstorm, grains hop a few centimeters above the ground in short, repeated bounces, dislodging more grains each time they land. What is this motion called?

During a dust storm, fine silt and clay particles are lofted high into the air and can travel hundreds of kilometers before settling. What is this transport mechanism called?

As a glacier slides over bedrock, rock fragments frozen into its base scratch and grind the surface beneath it, leaving fine rock flour. What is this process called?

Meltwater seeps into cracks in bedrock beneath a glacier, refreezes, and pulls entire blocks of rock loose as the ice moves forward. What is this process called?

The Grand Canyon in Arizona is over 1,800 m deep in places, with layered rock walls and a narrow inner gorge cut into hard rock at its base. Which agent cut this canyon?

In Yosemite Valley, California, waterfalls such as Bridalveil Fall pour from side valleys that end high above the main valley floor. Which agent left these side valleys hanging?

At Great Sand Dunes National Park in Colorado, dunes rise about 230 m above the valley floor, built from sand carried out of the San Luis Valley and piled against the mountains. Which agent built these dunes?

On the outer shore of Cape Cod, Massachusetts, sandy bluffs are retreating by about 1 m every year as the coastline is cut back. Which agent is eroding these bluffs?

In 1925, a mountainside above the Gros Ventre River in Wyoming collapsed in minutes, burying the valley floor and damming the river to form Lower Slide Lake. Which agent moved this material?

At the mouth of the Mississippi River in Louisiana, sediment carried from across the continent is deposited into the Gulf of Mexico, building a birdfoot-shaped delta. Which agent deposited this sediment?

The Ronkonkoma and Harbor Hill moraines form two ridges running the length of Long Island, New York, built from unsorted rock, sand, and clay left about 20,000 years ago. Which agent deposited these ridges?