Earth Science: Weathering, Streams, Drainage Patterns and Landforms

Weathering

The breakdown of rock.

Erosion

The breakdown and transport of rock or sediment by streams, wind, or ice.

Mechanical weathering

Physical breakdown of rock, such as frost wedging, exfoliation, or roots growing into cracks.

Frost wedging

Water enters cracks, freezes, expands, and pries the rock apart.

Exfoliation

Rock layers peel away due to pressure release during erosion.

Organic activity (root weathering)

Roots grow into cracks in rocks and help break them apart.

Chemical weathering

Rock chemically reacts with water and natural acids in rain.

Leaching

Removal of soluble components from rock, leaving behind a residue.

Oxidation

Chemical combination of iron with oxygen; contributes to the red color of rocks.

Dissolution

Rock dissolves completely in water, leaving no residue.

Carbonic acid in rain

Water (H₂O) and carbon dioxide (CO₂) form carbonic acid (H₂CO₃), which can chemically weather rock.

Three types of streams

Straight, braided, and meandering.

Straight stream

A simple stream with one channel.

Braided stream

A stream with shifting, interconnected channels that split and rejoin like braided hair.

Braided streams: gradient

Usually associated with a steep gradient.

Braided streams

Shifting channels can form small islands between branches.

Meandering stream

A highly sinuous or snaky river associated with gentle slopes or a gentle gradient.

Meandering streams: erosion and deposition

Erosion occurs along one part of a bend while deposition happens along another, so the channel shifts over time.

Canyonlands Maze District drainage

Dendritic stream pattern.

Canyonlands Grabens District drainage

Rectangular stream pattern.

Three ways streams carry sediment

Bed load, suspended load, and dissolved load.

Bed load

Particles rolling along the bottom of a stream underwater.

Suspended load

Particles floating throughout stream water.

Dissolved load

Dissolved atoms or substances carried in the water, rather than visible particles.

Dissolved load: seawater example

Dissolved salt remains when water evaporates, increasing salt concentration.

What do stream drainage patterns reflect?

The properties and structure of the underlying bedrock or land surface.

Rectangular drainage pattern

Streams make right-angle turns in fractured bedrock; channels run down and across.

Trellis drainage pattern

Long streams follow valleys between ridges, with short tributaries draining the ridges; associated with folded mountains.

Radial drainage pattern

Streams flow outward from a central high point, such as a volcano.

Dendritic drainage pattern

Branching pattern like veins in a leaf; common on horizontally layered rocks or rock without layering, such as granite.

Parallel or subparallel drainage pattern

Streams flow mainly in the same direction, often because they drain a sloping surface.

Differential weathering

Some rocks weather and erode more easily than others, producing features such as cliffs and slopes.

Resistant rock vs. weak rock

Resistant rock tends to form cliffs or cap rock; weaker rock erodes into slopes or shoulders.

Hoodoo

A pillar of rock formed by differential weathering, often with resistant cap rock on weaker rock below.

Cap rock

A resistant rock layer that remains on top while weaker rock beneath erodes.

Tafoni

Honeycomb-like holes weathered into rock.

Steps in arch formation

Resistant sandstone develops fractures (joints); weathering forms fins; rock beneath spalls away, forming an arch.

Joints

Fractures in rock that help begin arch formation.

Rock fins

Narrow rock walls formed by weathering along fractures before an arch may develop.

Sandstone landforms

Sandstone is a resistant rock that commonly forms steep cliffs.

Shale landforms

Shale erodes more easily and commonly forms slopes or shoulders.

Triassic and Jurassic red sandstones

Major cliff-forming rocks in Utah parks.

Navajo Sandstone

A major sandstone that forms large cliffs.

Entrada Sandstone

Sandstone associated with most arches mentioned in the notes.

Red shales

Relatively weak rocks that form slopes.

Why are many Utah rocks red?

Oxidation of iron.

Yosemite: evidence of glacial erosion

A valley with steep sides and a relatively flat bottom formed by glacial erosion.

Continental glaciation

Glaciation from a very large ice sheet covering broad areas.

present-day continental glaciers

Greenland and Antarctica.

How do continental glaciers spread?

Snow accumulates at high latitudes; thickening ice spreads outward radially.

Glacier accumulation, snow line, and wastage

Terms from the notes describing snowfall buildup, the snow-line boundary, and ice loss.

Glacial sediments

Rock and sediment picked up, moved, or left behind by glacial ice.

How thick can large ice sheets be?

The notes describe glaciers up to about two miles thick.

What do deposits of till reveal?

A glacier once flowed through the area, even if no active glacier remains.

Till

A mix of coarse boulders, cobbles, sand, and silt deposited by a glacier.

Glacial erratic

A large boulder carried and dropped by a glacier.

glacial erratics in New York City

Central Park.

Loess

Finely ground sediment; the notes describe it as finely ground sand.

Where can thick loess deposits occur?

Central China.

Moraine

A ridge or pile of glacial till, often marking the limit of a glacier's advance or the former glacier front.

How can a glacier build a moraine?

It pushes sediment like a bulldozer, leaving a pile or ridge near its front.

Glacial striations

Scratches on rock caused when glacier ice drags stones across the surface.

What can glacial striations show?

The direction a glacier flowed.

Ice age

A period when continental glaciers grow.

Major worldwide glaciations

recurring widespread glaciations roughly every 200-300 million years.

Pleistocene Ice Ages: beginning

About 2.5 million years ago

Pleistocene glacial cycles

Repeated advances and retreats of ice; the notes estimate about 20 cycles.

Glacial period vs. interglacial period

Cold phases with expanded glaciers versus warmer phases between glacial advances.

Pleistocene temperature fluctuations

fluctuations of about 6-10°C.

When glaciers grow, what happens to sea level?

Sea level falls as more water is stored in ice.

When ice sheets melt, what happens to sea level?

Meltwater returns to the oceans, causing sea level to rise.

Marine terrace and sea-level change

The notes describe terraces eroded when sea level was lower and submerged after sea level rose.

Isostatic rebound

The Earth's crust rises back up after the weight of a heavy ice sheet is removed.

How do microscopic marine shells help study past ice ages?

Their composition provides evidence of past ocean conditions and glacial climate changes.

Oxygen isotope ratio (¹⁶O/¹⁸O)

An isotope ratio that varies with ice volume and helps scientists interpret past climate.

Evidence for ancient climate from ice cores

Annual layers, oxygen isotopes, trapped air bubbles, sulfur, and pollen.

Where are ice cores drilled?

In thick parts of ice sheets, where longer records can be collected.

How are annual ice-core layers used?

They can be counted to help date the ice, much like tree rings.

Ice-core oxygen isotopes: seasonal clue

The notes associate winter ice with more ¹⁶O and summer ice with more ¹⁸O.

What do air bubbles trapped in ice reveal?

Samples of the ancient atmosphere.

What does sulfur in ice cores record?

Volcanic activity.

What does pollen in ice cores record?

Past plant ecosystems.

Radiocarbon in ice-core studies

The notes mention ¹⁴C dating of trapped gas bubbles.

Ice movement at the thickest sampling site

The notes describe mostly vertical rather than lateral movement.

Snowball Earth glaciation

episode around 700 million years ago.

Ordovician glaciation

episode around 440 million years ago.

Devonian cooling event

The notes list an event around 365 million years ago.

Permian glaciation

The notes place it around 245-260 million years ago.

What features did past glaciation help create?

The Great Lakes and Hudson Bay

What type of rock contains most caves in these notes?

Limestone.

How limestone caves form

Groundwater dissolves limestone through chemical weathering (dissolution).

Why is cave formation part of the hydrologic cycle?

Water moves into and through rock, dissolving soluble material and creating openings.

Carlsbad Caverns: cave rock

Limestone from a Permian reef containing fossils.

Carlsbad Caverns

about 300,000 bats.

Wind Cave: limestone age

Mississippian limestone.

Wind Cave: roof appearance

A mesh-like appearance caused by fractures and water seeping downward.

Wind Cave: predominant cave direction

Northwest, matching many of the rock fractures described in the notes.

Wind Cave: original entrance

About 20 inches wide, according to the notes.

Why can cave passages occur at different levels?

Water dissolves rock at different levels over time, creating passages of different shapes.

Jewel Cave: predominant passage direction

Northeast.