Erosion and Weathering / Glaciers

mleziva core

What distinguishes erosion from weathering?

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

Terracettes

Lines of small ridges on the side of a hill

Formed by soil creep

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

Mudflow

high moisture + rapid form of mass wasting

→ Glacial melting adds a massive amount of meltwater to the land. When this water rapidly flows down a slope with soil, it can cause powerful waves of debris + mud → lahars

i.e. lahars can be caused by volcanic eruptions bc glaciers on the volcanoes get melted

Avalanche

Rapid downward fall of snow/ice

Not a type of mass wasting bc mass wasting must be weathered rock material

Caused by excessive snow fall, sudden temp. changes, skiers

Leaching

Process of stripping nutrients from soil where groundwater/rainwater dissolves too many nutrients/minerals out of the soil.

Remedy: add fertilizer in smaller amounts, more often; add organic matter; have a better irrigation system to reduce waterlogging

Granular disintegration/spherification

The physical weathering of the outer surface of a coarse-grained rock so that it becomes rounded

Pervious + give examples

Type of rock that allows water + air to pass through

(Conglomerate, limestone, sandstone)

similar to permeable

Impervious rocks + examples

Type of rock that does not allow water + air to pass through (clay, though clay is porous)

Granite, marble, slate, shale

similar to impermeable

Porous

Rock that is able to hold water
e.g. vesicular external igneous rocks like pumice, scoria

Clay is porous although it is impervious (i.e. it can hold water, but it doesn’t let the water flow through easily)

Imporous

Rock that is unable to hold water

Milanchovitch Cycles

1. Eccentricity: how much orbit deviates from circle

2. Precession: wobble/direction of axial tilt

3. Obliquity: Angle of axial tilt

How do glaciers affect North America in the Ice Ages, present and future?

Ice Age:

• Weight of glaciers pushed land down → isostatic depression

• (pro)Glacial Lake Missoula → later led to the Scablands

• Erosional forces carved out the Great Lakes + other glacial landforms

• Abrasion from glaciers scraped off most fertile topsoil from Canadian Shield, but exposed mineral-rich veins

• Glacial till deposits, esp those from ground moraine, loess deposits, glacier lake beds, etc, are fertile

Present:

• Modern glaciers are rapidly in retreat/melting (Greenland + Antarctica + alpine glaciers)

• Immediately after the ice age, some coastal areas were flooded due to eustatic (global) rise in sea level bc of high volume of meltwater

• Eventually, the land rose up again after the pressure from glaciers was lifted → isostatic glacial rebound

Future:

• Disappearance of some ice caps

• water shortages in arid areas

• thawed permafrost can cause instability in building foundations

Isostatic rebound/readjustment

the rise of the land after the weight of the glacier is taken off. very slow + isolated to a specific area, not global

this forms a raised beach

Eustatic Sea Level Rise

global rise in sea level after the ice age

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.

Types:

1. Rock fall

2. Soil creep

3. landslide

4. slump

5. solifluction

What are the features of loess deposits?

• light dun/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 → fluvial transport

  • wind then carries these powder-like deposits beyond the outwash plain → aeolian transport

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

• **it is sorted, but unstratified bc the final depositor is wind, not water → does not form neat layers, but only smaller particles can be picked up causing it to be sorted

What does denudation mean?

the forces that lower the level of the land

i.e. weathering + erosion

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 + big jumbled mix of rocks bc it was carried by solid ice

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

What defines a drumlin?

a tear-shaped slope of glacial till

indicates direction of movement as glacier deposits

**glacial till = unsorted sediment!!

What constitutes an outwash plain?

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

(sorted = filtered by size of sediment, stratified = the different sizes have been clearly settled in different layers)

What defines a kame?

both continental & alpine
a) a steep mound of deposits formed by meltwater streams

b) a flat-topped mound of deposits formed by meltwater that evens out existing lateral moraines → gradation

all kame is sorted and stratified because it is deposited by meltwater → fluvial transport

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?

• type of physical erosion

• scraping or grinding of a bedrock by an ice sheet

• example of a feature produced by this action is striations

What is meant by plucking in glacial contexts?

• type of physical erosion

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

• happens bc the rock freezes onto the ice

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?

both continental and alpine

They are long, narrow lakes that were created by glaciers cutting through ground that is composed of bands 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

→ the hard bedrock is known as a rock bar

can also be formed by damming behind a reccesional or temrinal moraine

What is roche moutonnee?

both alpine & continental
a sloped outcrop of bedrock that is smooth on the end that the ice flow came from (upstream), and rough on the end the ice flow left (downstream)

• upstream end: higher pressure caused abrasion which grinded the bedrock smooth + created striations

• downstream end: lower pressure caused meltwater to freeze → freeze-thaw → plucking

occurs bc glacier flows over a bedrock

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

a deep spherical depression in the side of a mountain formed by a glacier. 

1. As the glacier builds in the depression, freeze-thaw causes rocks from the outer layer of the mountain face to break off and become embedded in the glacier

2. As the weight of the glacier causes it to slide around, more rocks get integrated and plucked

3. Finally, the rocks in the glacier deepen and widen the depression through abrasion.

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

  • approaches from a sloped, smooth side (abrasion) and ends on a jagged, steeper side (plucking)

  • glacier flows over bedrock

• drumlin

  • approaches from the steep side, leaves on the sloped tail → caused by change in upstream/downstream movement

  • glacier flows over glacial till

spillway

valley formed by meltwater (continental glaciation)

usually wide and shallow bc meltwaters carry a LOT of sediment

misfit streams

both continental + alpine
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.

can also occupy u-shaped valleys

eskers

long winding ‘snakes’ of sorted deposits left by meltwater

• super for road building bc of its permeability + porosity

• its skinny bc its formed by substreams in, on or beside the glacier

• sorted and layered bc fluvial transport

glacial ponding

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

Which glacial features are both alpine and continental?

For sure: striations, erratics, crevasses, moraines, glacial till,

Maybe: eskers, drumlins, roche moutonnee, ribbon lakes,  kame, misfit streams

Difference between striations and crevasse

Striation: a scratch left on the rock below the glacier

Crevasse: a crack in the glacier itself

How have glaciers benefited North America?

• Canadian Shield, abrasion exposed valuable minerals to the surface (although it also scraped away most fertile topsoil)

• Post-ice age isostatic rebound → new land resurfaced

• Fjords used as sheltered harbours

• Tourism

  • Great Lakes

  • The Rockies

    • Skiiing & snowboarding on mountains

    • mountain lakes (tarns)

• Energy

  • Hydroelectric power

    • Great Lakes

    • Waterfalls from hanging valleys

• Transport

  • Great Lakes

  • St. Lawrence River

  • The Rockies

  • Hudson-Mohawk Gap - a glacial-cut channel that connects to New York

• Freshwater/drinking water

  • Great Lakes

  • St. Lawrence River

• Fertile land:

  • Fertile soil deposits in Prairies + boulder clay plains around Canadian Shield (from glacial till)

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

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

  • glacial lake beds are fertile

• Transhumance → migration of herds/flocks

  • Ridges with pastures on the sides of mountains are good for raising cattle during warmer seasons

Ablation

loss of material from a glacier

How do glaciers move? Describe the process.

1. Glacial creep. The weight of the glacier causes slow movement, especially near the center of the glacier where it is the thickest → ice crystals inside the glacier shift and creep from the pressure of its own weight

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

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 → forms a glacier

2. freeze thaw on mountain expands and contracts the rock, causing fragments to break off

3. abrasion as glacier moves around the cirque in a circular motion (bc its so heavy)

4. plucking deepens + widens the cirque

5. 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.

6. The hollow left behind is a cirque.

alluvial fan

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

creates a large ‘fan’ of alluvial deposits

find 8+ glacial features (click on photo to zoom)

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

ice fall vs crevasse

crevasse:

both alpine & continental

both meltwater & solid ice

→ bc meltwater widens the crack after it is formed in the ice

Definition: a deep crack in a glacier caused by stress, a change in direction, steepness of ground, or entrance into a wider valley

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

• basal sliding:

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

• glacier creep:

  • ice crystals melt and refreeze in a cycle that causes it to crawl down a slope

  • exacerbated by higher pressure + temp

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, poljes, uvalas, etc

oxidation weathering

• chemical

• Iron → rust → forms red coloured rocks

• rusted rocks more susceptible to erosion

hydrolysis weathering

• chemical

• common with granite (anything with feldspar mineral)

• slightly acidic rainwater reacts with feldspar

  • creates clay (softer, smaller granules, susceptible to physical erosion)

hydration weathering

• combination of mechanical & chemical weathering

• mainly affects rocks with salt minerals

• water seeps into rocks and attaches to anhydrous salt minerals (mr yoo’s lab!!)

  • 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 created by it

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

• usually limestone

• creates underground rivers, sinkholes, caverns

• stalactites

  • hang down from ceiling of cave

• stalagmites

  • protrude upwards from ground

• pillar

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

• sinkhole

  • forms when a cave/cavern reaches the surface

  • aka doline

• uvala

  • a larger depression

• polijes

  • a collapsed cave

• hum

  • a small, steep mound that is formed in the final stages of karst topography. it was able to resist chemical weathering bc it is a piece of sturdy bedrock

*common in the Rockies

what affects the severity of mass wasting?

• angle of slope of hill

• gravity

• water presence

human factors: deforestation, mining, farming, urban development

aquifer

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

must be above a layer of impermeable rock

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)

what is a joint and how is it created

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

created by tectonic processes + release of pressure (exfoliation) + thermal contraction (basaltic columns)

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

landslide

medium moisture, fast form of mass wasting

→ debris falls in planear fashion (completely straight)

→ more moisture than rock fall

→ en masse

rock fall

fast + dry type of mass wasting

→ weathering causes rock fragments to fall off the side of a cliff and accumulate in piles (taluses/screes)

→ commonly caused by freeze thaw

slump

forms GULLIES
a slow speed, medium-humidity type of mass wasting
→ caused by heavy rain

→ water reduces friction btwn soil particles + adds weight to soil

→ debris falls in a curved path

soil creep

slow and dry type of mass wasting

→ causes leaning in the objects/land above (trees, buildings, infrastructure)

→ creates terracettes too

→ less than 1-2 cm/yr

solifluction

slow + high moisture type of mass wasting

slow movement of water-saturated soil down a non-permeable surface

• eg. permafrost in Arctic tundra

• forms lobes

another word for sinkhole

doline

spring

body of water fed by an underground aquifer that has at least 1 end where the water table is exposed at the surface and that emits a constant flow of water outside

artesian well

high → low pressure gradient of water on a slope naturally pushes water up a tube to allow for constant water flow

the aquifer must be a shallow syncline with impermeable rock underneath and above, and one or more ends of permeable rock exposed at the surface to allow water to enter

→ called an artesian basin

permeable rock

rock that allows water to pass through its joints

very similar to pervious except i think pervious rocks allow water to pass through their pores??

pretty interchangable imo

impervious rock

rock that is non-permeable; forms bottom and top of an aquifer

i.e. it doesn’t allow water or air to flow through

why is groundwater important for humans? 4 reasons

1. springs + wells decide settlement locations, especially in arid areas like deserts

2. provide water for cattle

3. has a role in irrigation

4. provides large source of drinkable water

what is a gully

a deep channel formed by slumps or water erosion

→ usually on hillsides with low vegetation so that the water can erode the hill without roots holding the soil together

terracette

formed by soil creep

looks like mini-steps/ridges on a hill

stalactite

deposits of mineral that build up into a structure that hangs down from the ceiling of a cave

stalagmite

deposits of mineral that build up into a structure that protrudes up from the floor of a cave

pillar

deposits of mineral (calcium carbonate) that build up into a structure that connects the floor of a cave to the ceiling

caused by karst topography

hum

small hills left in a cave by karst topography after the cave has gone

poljes

caused by collapse of a cave due to karst topography

→ different from sinkholes bc these are much wider and flat-bottomed. they also have extremely steep walls

uvala

a large depression caused by karst topography

→ usually the combination of multiple sinkholes/dolines