Earth Sciences 240A - Lecture 28 - Mass Movement

Introduction

It’s the gravity, stupid!

Economics

Most expensive of all natural phenomena

USA: $1.5 B/yr

Gravity

Nomenclature: Force of cohesion and friction = ‘inertia’ [Abbott]

Components

Perpendicular to slope

Parallel to slope

Angle of repose

Importance of lubricant (water)

Classification of Mass Movement Processes

Creep

Slow (~3-4mm/y); Regolith affected

Frost heaving; Salt heaving

Never associated with catastrophe

Debris Flows/Mud Flows

Wide particle size variation

High content water

May travel ~320 km/h

Lahars are in this category

Rock Falls

Free-fall of blocks

Vertical to near-vertical slopes

Commonly dislodged by frost, rain

Rock Slides

Motion from planes of weakness: Joints, foliation, faults

Most catastrophic

Examples

Frank Slide

Vaiont Slide

1963, Italian Alps

Construction Concrete Hydro Dam

Terrible geological site

Solution cavities in foundation rock

Increased side slope creep with filling of reservoir

1960: 1 million m3 slide

1963: creep 1 cm/d to 39 cm/d to 80 cm/d

240 million m3 slide

Over top of dam; ‘tsunami’ in reservoir

Subsidence

Vertical collapse Driven by gravity

Water usually plays a role

 

Categories

Human induced

Water, oil/gas, coal, etc.

Natural

Sinkholes, caves, Karst topography

Groundwater and Limestone

Rain:

H2O + CO2 = H2CO3

Weak carbonic acid

Limestone reaction

H2CO3 + CaCO3 = Ca2+ + 2HCO-3

Both attach to water molecules

Cavity forms plus Salactites/salactites

Karst topography

Salt Solution

Example: Lake Peigneur, Louisiana

Barge oil drill punched into salt mine

Rapid solution of NaCl

Plate Tectonics/Subsidence

Flooding of ‘failed arm’ of Red Sea action

Dead Sea area; flash flood

Basis for the Moses sea-parting?

 

Next

Prerequisite: Hydrosphere & Atmosphere