failure surface

Melissa Beukeboom @

Gravity is the force that pulls everything toward the centre of the Earth

Friction between soil particles must RESIST the pull of gravity

When a landslide occurs….

GRAVITY WINS!!

WHY?

What helps

gravity to win?

2. Erosion

3. Water content in soil

4. Disturbances like: Earthquakes

Volcanic eruptions

Machinery, traffic, mining

1. Type of sediment

ROCK PARTICLES

a.k.a. SEDIMENTS

WATER AIR ORGANIC MATTER

Let’s take a

closer look!1. Type of Rock Particles

(a.k.a. Sediment)

Rocks are weathered (broken down) by water, wind, and ice into smaller and smaller pieces called

Main types of SEDIMENTS:gravelsandsiltclay

SEDIMENTS

1. Type of Rock Particles (a.k.a. Sediment)

Gravel and sand grains are very angular in shape. Their sharp edges hold on to each other, increasing FRICTION and fighting GRAVITY.

What happens to these sediments when a landslide occurs?

1. Type of sediment (continued)

Clay particles are flat and fit together very tightly.

This prevents water from moving between clay particles easily.

Water pressure can build up in slopes made of clay.

1. Type of sediment (continued)

QUICK CLAYS

A SPECIAL CASE!!

QUICK CLAYS IN ONTARIO

We are here!

Ottawa & QuebecLEDA CLAY OR CHAMPLAIN SEA CLAY

Northern Ontario & Quebec

TYRRELL SEA CLAY

Do we have quick clays in Ontario?

YES!

2.0 x 10-9m or 0.000000002 m –

that’s small!!!

1. Type of sediment (continued)

The card house structure makes quick clay very stable….

Until the structure is disturbed!!

2. Erosion

When a slope is over-steepened, it becomes unstable

Rivers erode the base of slopes and make them too steep…making it unstable

RIVERRIVERRIVERRIVERRIVER RIVER

3. Water Content

Too much water added to soil, pushes the sediment particles apart.

The particles lose contact with each other…therefore they lose FRICTION!

So GRAVITY wins!

4. Disturbances

Disturbances also push particles apart, causing them to lose contact with each other

They lose FRICTION, so….

So GRAVITY wins!

4. Disturbances include:

Volcanoes!

4. Disturbances include:

Earthquakes!

Volcanoes!

4. Disturbances include:Earthquakes!

Construction

Volcanoes!

4. Disturbances include:

Volcanoes!Earthquakes!

Construction

Heavy Traffic

4. Disturbances include:

Volcanoes!Earthquakes!

Construction

Heavy Traffic Deforestation

Let’s re-cap…Landslides occur when the land is unstable…allowing

GRAVITY to win!

Instability depends on: The type of sediment

Water content in the soil

Erosion over-steepening the slope

A major disturbance

When a landslide occurs…

It can be fast

It can look like “the wave” or falling dominos

The “domino effect”

To conclude…here is a bit humour…

or slow

Imagine the people are sediment particles

It’s time to slip, slide and away