Erosion and Weathering

mleziva core

What distinguishes erosion from weathering?

Erosion refers to the transportation of weathered rock fragments, while weathering involves only breaking up rock masses

What does mechanical weathering mean? list 3 types

It involves breaking up rocks into smaller fragments without changing their chemical composition

aka physical weathering

1. frost action/freeze-thaw

2. root wedging

3. exfoliation

What is meant by chemical weathering? list 3 types

It involves the alteration of rock through actual chemical changes in the minerals' composition.

1. carbonation/solution

2. oxidation

3. hydrolysis

4. hydration (this is both)

5. plant/animal (potential for both sides)

What is mass wasting? list 5 types

The downhill movement of weathered rock materials through creeping, sliding, slumping, flowing or falling.

What are the features of loess deposits?

• light dune/yellow colour

• fine-grained silt (although up to 1/3 can be clay, which is even smaller than silt)

• carried into outwash plain by meltwaters as glacier melts/ablates

• wind then carry these powder-like deposits beyond the outwash plain

• when dry, can maintain steep slopes bc of its angular fragments

• unconsolidated + unstratified bc the final depositor is wind, not water

What does denudation mean?

the forces that lower the level of the land

i.e. weathering + erosion

How do rivers influence landscape formation?

Rivers create valleys and plains through erosion, transportation, and deposition.

What are the defining characteristics of the three sections of a mature river?

The upper course is characterized by erosion, the middle course focuses on transporting sediment, and the lower course emphasizes deposition.

What are the three main processes in glacial erosion?

abrasion

plucking

freeze-thaw

What features are associated with alpine glaciation?

horn/pyramidal peaks, tarns, cirques, aretes, u-shaped valley, hanging valleys, ice falls, col, alps?, finger or ribbon lakes, truncated spurs, waterfalls

What’s the difference btwn glacial till and sediments from outwash plains

glacial till is unsorted bc it was carried by solid ice

stratified deposits were sorted by meltwaters and carried into the outwash plains

What defines a drumlin?

It is a smooth, elongated hill created by the accumulation of glacial till, distinctly formed by glacial activity.

What is an esker?

A long, winding ridge formed by sediment deposition in a meltwater river, which remains after glaciers retreat.

What constitutes an outwash plain?

This is a flat area formed by sediments deposited by meltwater flowing from a glacial front, producing sorted and stratified sediments.

What defines a kame?

A mound or hill resulting from the accumulation of sand and gravel deposited by glacial meltwater, found at the edge of a glacier; it differs from a terminal moraine, which is a pile of debris marking the glacier's furthest advance.

What characterizes a terminal moraine?

It is a pile of debris that accumulates at the glacier's front edge, marking the maximum advance of the glacier.

What is an erratic in glacial contexts?

This term refers to a solo rock carried and deposited by a glacier, which often differs in size and type from the local bedrock. It is a mix of different kinds of sediment & rock.(unsorted)

What does neve refer to?

It describes the granular snow that compacts and transforms into glacial ice over time, found in the upper regions of a glacier.

What is abrasion in the context of glaciers?

scraping or gouging by an ice sheet and the debris it moves

example of a feature produced by this action is striations

What is meant by plucking in glacial contexts?

This process refers to the removal of pieces of bedrock by ice, leading to the formation of features such as U-shaped valleys.

What are striations?

These are scratch marks or grooves found on bedrock, created by the abrasional action of debris embedded in the glacier's base.

What are ribbon lakes?

They are long, narrow lakes that were created by glaciers cutting through ground that is composed of layers of soft and hard rock outcrops. the soft rock gets eroded into long narrow depressions that turn into lakes after the glacier melts. on a map these often look like claws

What is roche moutonnee?

Occurs when an outcrop of hard rock is smoothed on the side facing the ice and plucked by freeze thaw action on the side facing away

What is a Graduational Force?

A force that levels out rock structures.

Why do Ice Ages occur?

a) volcanic eruptions lower global avg temp bc the ash prevents UV rays from getting into the earth

b) variation in solar energy emitted from Sun

c) Milankovitch Cycles:

Eccentricity: Variation in orbit shape (spherical vs elliptical)

Tilt: Variations in angle of earth’s tilt

Precession: Variation in wobble, aka direction of tilt

d) reduction in CO₂ on Earth

What is the difference between alpine and continental glaciation?

alpine is formed at high altitudes; continental is widespread and occurs across over a large land mass

Where do alpine glaciers tend to form?

on fold mountains near the coast (high precipitation) so that snow can accumulate enough to squash into ice

onshore winds bring wind directly to the mountains

List all the glacial landforms in this photo + the type of glacier that produces them.

1 is a Pyramidal Peak; 2 is an Arête; 3 is a Cirque; 4 is a Tarn; 5 is an Alluvial Fan; 6 is a Ribbon Lake; 7 is a Truncated Spur; 8 is a Misfit Stream; 9 is a Hanging Valley; 10 is a 'U' Shaped Valley

alpine glacier (except misfit stream is more continental)

Cirque

round depression on side of mountain created by freeze thaw of a glacier. the glacier plucks out the side of the mountain over time.

Tarn

if the cirque becomes full of water, this lake is called a ___.

Horn/mountain peak

sharp top of a mountain formed by multiple cirques cutting out the sides

What’s the difference between a drumlin and a roche mountonee?

glacial till in drumlins vs bedrock in roche moutonee

direction of skew as glacier approaches

• roche mountonee ends jaggy, abruptly

• drumlin ends gradually

spillway

valley formed by meltwater (continental glaciation)

misfit streams

streams that occupy spillways formed by meltwater from glaciers. these streams are so much smaller than the og glacial river that formed the spillway that they look out of place.

eskers

long winding ‘snakes’ of sand and gravel deposits left by a glacial stream

super for road building

glacial ponding

continental; body of water that forms from leftover glacial meltwater that is unable to flow away

Which glacial features are both alpine and continental?

striations, crevices, till, terminal moraine, erratics

Difference between striations and crevices

Striation: a scratch left on the rock below the glacier

Crevice: a crack in the glacier itself

How have glaciers impacted North America?

• Canadian Shield, erosion scraped away most fertile soil, although it also exposed valuable minerals to the surface

• Great Lakes & St. Lawrence River

  • tourism + transport + freshwater + hydropower

• The Rockies

  • tourism + transport

• Fertile soil deposits in Prairies + plains of clay + sand around Canadian Shield

• Good drainage + quality soil + gentle rolling hills from glacial till South Ontario

• Build-in fertilizer in till from limestone-rich bedrock

• Erosion of mountains gradually causes isostatic rebound

• Fjords used as sheltered harbour

Ablation

loss of material from a glacier

How do glaciers move? Describe the process.

1. Glacier creep. The weight of the glacier causes slow movement, especially near the center of the glacier where it is the thickest → internal flow.

2. Basal sliding. Internal streams (meltwater) + warmth of earth along the bottom of the glacier causes fast sliding.

accumulation

addition of material to a glacier

How do you know if a glacier will retreat or advance?

accumulation > ablation → advance

accumulation < ablation → retreat

accumulation = ablation → net movement zero, internal streams exist

col

a cirque that separates an otherwise continuous mountain ridge

arete

sharp ridge that separates cirques

How are cirques formed?

1. Snow fills a depression on a mountain, compacts into neve, later into ice → glacier

2. freeze thaw on mountain expands and contracts the ice, widening + deepening the depression by plucking the rock below

3. Glacier grows and continues to expand the depression, until it is too heavy to stay on the side of the mountain and starts to creep out. The hollow left behind is a cirque.

alluvial fan

special formation of deposit formed when a high-pressure, fast mountain stream suddenly enters a flat, open plain and loses velocity.

creates a large ‘fan’ of alluvial deposits

find 8+ glacial features

medial moraine (ii) truncated spur (iii) hanging valley (iv) cirque (v) pyramidal peak (vi) arête (vii) snow field (viii) lateral moraine.

What are the key features produced by continental glaciation?

• smoothed/rounded hills

• hollows, which form lakes (in soft outcrop of rock)

• roche moutonnée (harder outcrop of rock)

  • entirely bedrock

• craig and tail (e.g. volcanic rocks)

  • part bedrock, part glacial till

• drumlin

  • entirely glacial till

• moraine

  • terminal, lateral, medial, ground moraine

• kettle lakes

• outwash plains

• erratics

• potholes?

alp

• a nook on the side of a valley glacier that provides fertile grass for grazing cattle during the summer

• during the winter, cattle get moved to the pastures at the bottom of the valley

  • transhumance

• its below the snow line but above the valley line

• Switzerland, Norway, other mountainous countries

transhumance

movement of cattle from higher glacial pastures to lower pastures at the bottom of a glaciated valley, and vice versa

these valleys have rich pastures for grazing

how are eskers formed

substreams underneath the glacier formed from meltwater carry deposits that it unloads when the glacier stops or retreats. this creates thin, snake-like deposits of stratified sediment called eskers.

→ it’s layered bc the meltwater can sort sediments by size

ice fall vs crevasse

crevasse: a deep crack in a glacier caused by stress or change in direction or steepness of ground

ice fall: looks like a frozen waterfall; glacier has many crevasses and cracks all over in this area bc the glacier had to squish into a narrower channel or experience a change in steepness

which part of the glacier moves the fastest, and why?

center of the glacier

• sides experience more friction

• immense pressure lowers melting point of ice → more meltwater at bottom of glacier → basal sliding → faster movement in center

freeze thaw weathering

• physical

• water enters cracks in rock, freezes, expands → widens cracks

  • if water melts and refreezes, over time this can split the rock into pieces

  • forms angular fragments which accumulate at the bottom of a hill → talus/scree

exfoliation/spheroidal weathering

• physical

• most common in arid areas w/ high temperature fluctuation (aka hot deserts)

• rapid swing in temp causes different minerals in the rock to contract + expand at different rates → outer layer separates from the inside

  • over time, layers of rock peel off

• Related to spheroidal weathering bc:

  • water (rain) erodes rock into a round shape over time by peeling off the weakened outer layers

    • bc water rounds off any surface features and smooths the rock out

root action/root wedging

• physical weathering:

  • vegetation grows in the cracks of a rock → widens the crack as the plant grows

    • eg: tree roots, lichens, mosses, bush roots

**NOTE: vegetation could also reduce soil erosion because it regulates the temperature + binds soil together → both positives and negatives with plants on rocks

carbonation or solution weathering

• chemical weathering

• limestone most common

• slightly acidic rain is made when CO₂ dissolves into rainwater (H₂CO₃ or carbonic acid)

  • the carbonic acid reacts with limestone to produce a new compound that is soluble in water → easily eroded

• affects joints & bedding planes in the rock

• causes karst topography

  • caverns, underground rivers, sinkholes, etc

oxidation weathering

• chemical

• Iron → rust → forms red coloured rocks

• rusted rocks more susceptible to erosion

hydrolysis weathering

• chemical

• common with granite

• creates clay (softer, smaller granules)

• uses water to break down granite

hydration weathering

• combination of mechanical & chemical weathering

• mainly affects rocks with salt minerals

• water seeps into rocks and attaches to anhydrous salt minerals

  • increases pressure + causes swelling

    • → internal stress, fractures, physical breakdown of rock

What is the typical rule for which type of weathering affects the dif types of rocks?

sedimentary → physical/mechanical

igneous or metamorphic → chemical

limestone exception!

which type of climate is chemical weathering most commonly in?

warm + humid bc chemical reactions occur faster at higher temps & moisture levels

karst topography + features

• a landscape formed by the dissolution of soluble rock through chemical weathering

• usually limestone

• creates underground rivers, sinkholes, caverns

• stalagtites

  • hang down from ceiling of cave

• stalagmites

  • protrude upwards from ground

• pillar

  • mineral deposit that connects the floor and the ceiling in a cavern

*common in the Rockies

what affects the severity of mass wasting?

• angle of slope of hill

• gravity

• water presence + amount

aquifer

underground layer of permeable rocks that store groundwater (water from rain + precipitation over the years that collects underground)

extremely good quality source of water

source of wells + springs

clint

flat topped ridge in limestone after carbonation

grike

deep + narrow groove in limestone caused by carbonation

plant/animal chemical weathering

• plants absorb minerals from soil

• bacteria break down minerals when in water

• decaying plants produce organic acids → breaks down minerals further

**chemical weathering most common in humid + warm climates

grike vs clint vs joint

clint: flat topped ridge in limestone after carbonation

grike: deep + narrow groove in limestone caused by carbonation

joint: crack in the rock where the rain enters (dif. from faults bc joints are stationary wheras faults always move)

joint

crack in the rock where the rain enters (dif. from faults bc joints are stationary wheras faults always move)

which human activities affect mass wasting, and why?

• deforestation

• mining

• farming

• urbanization (construction of towns)

all of these increase the instability in slopes.

how can humans reduce their effect on mass wasting?

• deforestation:

  • if we cut trees, replant them

  • sustainable usage of natural resources

• settlement:

  • build on solid foundations/bedrock → not limestone!!!!

  • don’t build on steep slopes

  • proper drainage systems to not oversaturate our soil

  • terraces (aka stairs) instead of flat slopes may help reduce gravity’s weathering of soil

• mining:

  • if we close a mine, restore it back to the way that it was as closely as possible

  • remove heavy metals + pollutants from mine water before reintroducing into the ecosystem

• farming:

  • improve drainage systems to redirect excess water away from the soil

  • replant trees or shrubs with deep roots on slopes to hold the soil together

mudflow

landslide

rock fall

slump

soil creep

solifluction