5. An area of Texas near the end of the last ice age had a wet climate. Infiltration of rainwater was occurring at areas with depression. Scientists infer that depression was an area where slightly acidic rainwater collected and infiltrated into the sandstone. Describe the effect that the slightly acidic infiltrating water had on the calcite cement holding the sandstone together.

Correct Answer: The calcite cement would be chemically weathered (the chemical reactions cause breaking of existing bonds of the compounds and formation of new bonds thus leading to weathering) and removed by infiltrating water.

9. The diagram below shows a meandering stream flowing across nearly flat topography and over loose sediments.

If arrow length represents stream velocity, which diagram best shows the relative stream velocities in this section of the stream?

A)

B)

C)

D)

Correct Answer: Option C

The stream velocity is higher on the outward side and lesser on the inner side of the stream. And the outer and inner side of the stream change as the stream changes direction. Option C correctly depicts the stream velocity, with bigger arrows representing the stream velocity on the inner and outer side.

Hence, options A, B and D are incorrect.

1. Which statement best describes sediments deposited by glaciers and rivers?

A) Glacial deposits and river deposits are both sorted.

B) Glacial deposits are sorted, and river deposits are unsorted.

C) Glacial deposits are unsorted, and river deposits are sorted.

D) Glacial deposits and river deposits are both unsorted.

Correct Answer: Option C - Glacial deposits are unsorted, and river deposits are sorted.

Glacial deposits are composed of different amounts and shapes of till. Till is a general term used to describe all the unsorted rock debris deposited by glaciers. Till is composed of rock fragments ranging from clay to boulder size. Till is generally identified by being unsorted (all the rock is jumbled together) and unlayered. The glacier will often carry large boulders, sometimes as large as cars or small homes, as they advance. When the glacier retreats, these large boulders are left behind, often dropped among much smaller glacial till. These large boulders are called erratics. Since erratics are rarely derived from the local bedrock, identifying the source rock for the erratic can tell you about the direction the glacier travel from.

Glaciers are not merely large lumps of ice that flow across the ground. The leading edges of glaciers, especially the larger continent-spanning ice sheets, consist of large outwash streams that carry the meltwater away from the glacier. These outwash streams deposit all manner of debris, but because of its water transport, this debris is layered and well sorted. This makes outwash deposits more easily distinguished from glacial till. Many times the meltwater flows for some distance under the glacier, following a sinuous (snake-like) path. The water continues to deposit sediment, and as the glacier finally retreats, a long sinuous ridge is left behind. These ridges are called eskers.

Another feature formed under the glaciers are drumlins. Drumlins are tear shaped hills formed of till. The drumlin forms with the tapered end pointing in the direction of flow of the glacier. Exactly how the drumlin forms is unknown as we have been unable to observe their formation under present day ice sheets. Drumlins can range in size from small (a few tens of meters in length) to large (over hundreds of meters and even kilometers long).

The most common of glacial features are the moraines. Moraines are bodies of unsorted till that form on the side or the leading edge of a glacier. There are several types of moraines that can be identified depending on their location on the glacier. Lateral moraines form on the sides of valley glaciers. They are composed of rock debris eroded from the mountains that surround the valley glaciers. When the glacier retreats the lateral moraine forms ridges that separate glacial valleys.

Delta growth indicates that a river delivers sediment to the shore faster and in greater volume than marine processes can remove the load. During the delta-building process, sediment is distributed in such a way that the feature develops a unique form. Under normal discharge conditions, sediment remains within the channel until it reaches the river mouth. No lateral dispersion of the load occurs on the subaerial delta plain, and because river velocity is so low, waves and currents spread the fine-grained portion of the sediment laterally along the delta front. During floods, however, suspended sediment and organic matter are deposited in the interfluve areas, causing those portions of the subaerial delta to aggrade. The high river velocity at the mouth offsets wave and current action, allowing sediment to be transported farther seaward. This facilitates accumulation at the delta front and causes the subaqueous delta to prograde.

The dispersal of sediment during floods and normal discharges creates a well-defined horizontal and vertical depositional sequence. On the subaerial delta plain, silts and clays accumulate vertically in inter-distributary zones. At the mouths of deltaic rivers, marine processes rework fine-grained sediment, but more coarse deposits of sands and silts usually build forward while maintaining a steep seaward slope. Smaller clay particles pass over the delta slope and are deposited on the continental shelf in front of the subaqueous delta plain. Therefore, in a horizontal sense, many deltas have silty, organic-rich deposits in their subaerial portion, though channel sands and levee deposits interrupt the fine-grained interfluve sequence. More coarse sediment is deposited at the river mouth, and very fine-grained materials (clays) accumulate beyond the delta front. The vertical sequence is essentially the same with marine clays at the lowest elevation (greatest depth), silts and sands at nearshore depths, and silts, clays, and organics—along with associated channel and levee sands—at the highest (subaerial) elevations. This model of alluviation does not accommodate very coarse (gravel and sand) deposition on the subaerial delta plain, which provides the special deltaic types known as fan deltas or braid deltas (see above), but it is representative of most of the major deltas of the world.

2. A stream is flowing southwards in New York State. When there is a slight change in direction, the velocity of the stream changes. When this stream’s velocity decreases from 300cms/sec to 200cms/sec, which size sediment will be deposited?

A) Cobbles

B) Silt

C) Sand

D) Clay

Correct Answer: Option A – Cobbles

From the Earth Science reference table, we have the following data:

According to the Particle Size to Water Velocity chart, cobbles will be deposited in a stream that travels slower that about 200cm/sec. If a stream's water velocity is faster than 200 cm/sec, it will carry a cobble down a stream. If a stream travels at a rate of 200cm/sec the particles that will be carried by the stream are pebbles, sand, silt, and clay.