Risks & Disasters Final Exam Notes
Three types of movement:
o Moves through air, lands at base of slope
o Triggered by vibration, ice or vegetation
o Rapid process
o Movement in contact with underlying surface
o Ex. Rockslide, translational slide slump, slip
o Plastic or liquid movement in water and sometimes air
o Mass breaks up and flows during movement
o Ex. Solifluction, mudflow, debris flow, debris, snow avalanche
Landslides are mainly a result of a change in the forces on the slope:
o Uplift and erosion
o Cause the rock material to move faster down slope
o Acts as friction force that is against the motion of rock materials
Geographic Distribution: distribution of landslide-prone materials in Canada:
Landslides are most common in mountainous areas, the St. Lawrence Lowland, and river valleys on the
western interior plains (British Columbia, Yukon and Alberta)
Materials particular prone to land sliding include lacustrine and marine silts and clays, cretaceous shales,
Quaternary volcanic rocks.
Three factors are expected to increase the occurrence of landslides in some areas of the world in this century:
Urbanization and development will increasingly expand into landslide-prone areas
Tree cutting will continue in landslide-prone areas
Changing global climate patterns will result in increases in precipitation in some regions
Prediction and Warning of Landslides:
slopes and seismic activity
o consider over steepened slopes enhanced by seismic activity
geology and structure
o consider soluble rocks or those weakened by water, bedding planes
surface water build up
o consider the water conditions and springs, pools of standing water
topographic and vegetation features
o consider scarps, old landslides, hummocky and young vegetation
o consider equipment embedded in slope, vegetation stems, and cracked road surfaces
Techniques for Preventing Landslides:
o interceptor drains, capture runoff and take away from slope, repair pipes and wells by draining
or pumping water out
slope reduction o reduce instability by introducing benches and terraces, remove falling material
engineering to resist mass movement
o armour surface with concrete, crushed rock to reduce erosion
engineering to mitigate damage
o netting or wire fencing, rock sheds or tunnels
Case Study: California
The 2005 landslide that took place in La Conchita, California started as a slump and then turned into a
flow that buried 30 homes and killed 10 people. The landslide took place above the sensors that were put
in place after the 1995 landslide; therefore a warning was not able to be put in place.
Social adjustment would be the best approach because even though sensors were put in place after the
1995 landslide, they still were unable to provide a warning to the residents. Also imputing engineered
techniques like netting or wired fences would cost a lot of money, and would not necessarily work due to
the fact of how steep the slope is and how weak the sedimentary rocks are.
La Conchita is a part of the “landslide capitals” in southern California and the sea cliff that is exposed
consists of older landslide deposits and weakly cemented sedimentary rocks with little shear strength.
With heavy rainfall, it is likely that a landslide may occur in the future.
more landslides are likely to occur as uplifts of 4 to 6 meters occur every thousand years, and these uplifts
occur when landslides take place. With the steep surface, low shear strength and large amounts of water,
it is likely that these landslides will continue.
o Presence of steep, high slopes
o Presence of weak rocks
o Presence of numerous historic and prehistoric landslides
o Periodic prolonged and intense rainfall
o Stabilize the slope
o Change the land use
o Install an effective warning system
Region drained by a single stream. Each stream thus has its own drainage basin that collects rain and
A large river basin, such as the Red river basin, is made up of hundreds of small watersheds drained by
smaller tributary streams.
Often associated with intense rainfall events such as those that occur with convective thunderstorms
Usually account for most flood-related deaths since they are highly unpredictable and little warning is
o Example: Big Thompson Canyon in Colorado
Often cover large areas in extensive river valleys with flat topography
Occur following periods of prolonged rainfall or large snowmelt
o Example: Mississippi River flood of 1993
o In Canada, southern Manitoba Discharge:
The volume of water that moves through a cross-section of a river per unit of time
It is calculated by multiplying the cross-sectional area of the water in the channel by the flow velocity, and
is commonly reported in units of cubic metres per second.
Three channel patterns:
o Large number of intersecting active channels
o Two or more channels and intervening stable islands where sediment is temporarily stored
o Single channel shaped like a snake
Use of hydrograph:
A hydrograph is made by installing a recording gauge to:
Obtain a continuous record of the water level (or stage)
This record is then used to produce a (b)stage-time graph
Field measurements at various flows provide a (c) stage-discharge graph
o Combining stage-time graph and stage-discharge graphs make the final hydrograph
In managing the flood hazard it is important to determine the frequency of flooding. Planning and land
use are often dependent on the predicted interval of flood events.
Often, the bigger the flood the longer the return interval. Floodplains can be mapped based on a 20-year,
50-year, or 100-year flood.
Magnitude & Frequency of floods:
Smaller floods may be produced by less intense storms that occur more frequently, and larger floods
produced by intense storms may happen less frequently.
Determined by the following equation and plotted to create a discharge-frequency curve:
o R = (N+1) M
The modification of the stream channel such as straightening or deepening. This often occurs in urban
areas where the stream is fitted to the built structures.
Channelization can have a number of impacts of the stream channel:
o Increase the possibility of flash floods
Which are shorter duration and larger in volume
o Increase in frequency
Processes that initiate fire:
o Lightning strikes
o Combination of intention and accident Limiting factors:
o Plant material, human material and structures
o Found in the atmosphere
o Includes lightning and human sources
General phases of wildfires:
The fire process has been broken down into a series of phases. These phases include:
o temperature and water content favour ignition
o preheating and pyrolysis (dividing fuel molecules and creating fuel gases for ignition) exists
o ignition can be caused by lightning, volcanic activity or humans
o combustion liberates energy and is dependent on a fuel source
Heat Transfer occurs through
o conduction (molecules)
o radiation (electromagnetic waves)
o convection (heated gases, temperature differences)
Extinction occurs when combustion ceases and there is insufficient heat or fuel to sustain combustion.
Role of wind:
cold front winds (high speed winds) help produce large scale wildfires
localized winds with high pressure air masses may move the fire down mountain-sides
fires are also encouraged by warm dry wind that increase temperature to 25°C with low humidity
cooler winds sucked into the base of the fire and growth continues
Development of Fire maps to predict risk:
These are based on accounts of current and antecedent weather, fuel types, and both live and dead fuel
Related maps determine lightning ignition, Haines Index (potential for wildfire growth), and weather maps
Ecological Role of fire in the forest:
When lightning hits dry fuels, grass, the result is fire. Lightning sparks regular burning
Over millions of years pants and animals have evolved with fire
Creative, life-giving force
Adjusted their life cycles and existence to the rhythm of fire
Many species that depend on fire
Burns to the ground every few decades, then grows back from the roots
Produces a whole new crop of seedlings
Native Americans used fire to burn their crops and promote seed growth for newer crops
Management strategies & results:
Codes and regulations
Fire management: changing attitudes:
A greater recognition of the role of fire in maintaining ecosystems and the danger of allowing too much
fuel to build up in forest and prairie ecosystems. Control programs shifted to letting natural fires burn and only controlling human-initiated fires.
Spread of Disease:
Population is not immune and includes carriers
Susceptibility to disease increases through conditions such as malnutrition
Physical events such as sewer and water main rupture resulting in fecal contamination
Lack of routine programs of disease control which spread endemic diseases such as cholera
Overcrowding in refugee camps which increases human contact and poor sanitation
Outbreak: simultaneous, related occurrence of several cases
Epidemic: uncontrolled outbreak of communicable (infectious or contagious) disease
Pandemic: international or wide-travelling simultaneous epidemics of the same condition
Epidemiology: study of distribution and determinants of health-related events in human population
The agent: the disaster
The environment: that which it affects
The host: affected people
o This disease is spread by rodents completing a cycle of bacillus spread from fleas to rats and onto
o It is characterized by a swelling of the lymph nodes, infection, and pneumonia leading to high
fever, delirium, vomiting, bleeding, and finally death.
o There were no noticeable groups that had greater vulnerability.
o All were affected with no specific target although there were incidences of persecution for
groups such as the Jewish and Gypsy populations as they were believed to be the carriers of the
o Cholera is a water-borne disease that comes from sewage and contaminated rivers often within
urban and rural water supplies.
o Cholera is an acute, diarrheal illness caused by infection of the intestine with the bacterium
Vibrio cholerae and is transmitted by contaminated food or water.
o Often mild and without symptoms, but can be very severe.
Role of Geography
o Mapping techniques were used to find the source of the disease.
GIS in controlling disease
o For locating the source and tracking the spread of epidemics.
o It is transferred through exchange of infected body fluids including blood and semen
o An assortment of disease manifestations related to the failure of the immune system Vulnerability
o It was originally believed that vulnerability was limited to homosexual activity, intravenous drug
use and haemophiliacs. Today the vulnerability is linked more to poverty.
Bird Flu and Influenza Pandemics:
o This disease became evident in 1997 when there was a large death of poultry in Hong Kong with
100% mortality. It was combated by killing all of the poultry. The most recent outbreak began in
o Wild birds worldwide carry the viruses in their intestines but usually do not get sick from them.
It is very contagious among birds but the H5N1 virus does not usually infect humans. Recently,
there have been human cases of H5N1 infection in Thailand and Vietnam.
o In general the spread of the H5N1 virus from person to person is rare and the spread has not
continued beyond one person. Presently, the death rate is about 70% or in other words, more
than two-thirds of those that become infected die.
o To date there have been about 100 deaths, primarily