Unit 5 Mini Case Studies Flashcards
deep sigh
4 examples of volcanic hotspots
Hawaii
Iceland
Azores
Tristan
Example of divergent (constructive) boundary
African and South American plate
Example of convergent (destructive) boundary
South American and Nazca plate
Example of conservative boundary
North American and Pacific plate
Example of convergent (collision) boundary
Indian and Eurasian plate
Main ocean ridges
Juan de Fuca
Central Indian Ridge
Chile Ridge
Main ocean trenches
Puerto-rico Trench
Mariana Trench
Java Trench
The Indian subcontinent in fold mountain building
Moved rapidly north in the last 70 million years colliding with the main body of Asia. The Tethys ocean has been lost between them due to subduction beneath Asia. In the collision zone the continental crust is thickened because Asis overrides India and it is the crustal thickening that results in the uplift of the Himalayan mountain range.
The Andes in fold mountain building
Formed as a result of the subduction of oceanic crust under continental crust. Are the highest mountain range in America with 49 peaks over 6000m high. Contain many active volcanoes. They comprise of a central core of granitic rocks capped by andesitic volcanoes. To the west of the central core, along the coast are the deformed rocks of the accretionary wedge and to the east of the central core are sedimentary rocks that have been intensely folded. Present subduction, volcanism and seismicity indicate that the Andes are still actively forming
Volcanic island arc examples
Most are located in the Pacific. Also occur in the western Atlantic where the Lesser Antilles (Caribbean) and Scotia arcs are formed at the eastern margins of small oceanic plates. The Lesser Antilles (Eastern Caribbean) Arc shows all features of a typical island arc. In the Eastern Caribbean the trench associated with subduction is filled with sediment from the Orinoco River. These sediments have been deformed and folded into the Barbados Ridge. The Lesser Antilles, the islands of Trinidad, Tobago and Barbados are the top of the subduction complex. Volcanic island arcs such as those in the Caribbean from Grenada to St Kitts are above sea level
Rockslides example
In 1959 the 6th strongest earthquake to affect the USA occurred in Montana. Close to the epicentre in the Madison River valley, a slope of schists and gneiss with slippery mica and clay was supported by a base of dolomite. A huge volume of rock, 400 metres high and 1000 metres long slid into the valley. 80 million tonnes of material moved in less than a minute. The Madison River was dammed and a lake 60 metres deep and 8 km long was created
Sheetwash examples
Occurs in the UK on footpaths and moorlands. During the Lynmouth floods of 1952, sheetwash from the shallow moorland peat caused gullies 6 metres deep to form. In the semi-arid areas of SW USA it lowers surfaces by 2-5 mm per year compared with 0.01 mm per year on vegetated slopes in a temperate climate.
Deforestation in Haiti
Haiti has experienced severe deforestation due to factors including logging and agricultural expansion. The lack of vegetation has led to increased soil erosion and landslides mostly during hurricanes and heavy rainfall events
Terracing in the Philippinrd
In mountainous regions of the Philippines, terrace farming has been implemented to reduce the slope angle and prevent erosion. This traditional agricultural practice helps stabilise slopes and minimises the risk of landslides
Urbanisation in Rio de Janeiro, Brazil
The steep slopes surrounding Rio de Janeiro have experienced landslides especially in areas with rapid urbanisation and inadequate infrastructure. Deforestation, improper construction practices and the growth of informal settlements have contributed to slope instability
Slope stability in Hong Kong
Hong Kong has faced challenges related to slope stability due to its hilly terrain and high population density. Engineering such as retaining walls and slope reinforcement have been implemented to reduce the risk of landslides in urban areas
Slope failure in Oso, Washington, USA
The Oso landslide in 2014 was triggered by heavy rainfall causing the collapse of a saturated hillside, burying homes and claiming lives. The area had a history of logging and land-use changes which also contributed to the instability.
Slope stabilisation in the Alps, Switzerland
In the Swiss Alps, where steep slopes are prevalent, measures have been taken to stabilise the slopes and mitigate the risk of avalanches and landslides. These include the installation of protective structures, afforestation and controlled rockfall prevention
Coastal erosion in Indonesia
Coastal areas in Indonesia have experienced increased erosion and landslides due to factors such as deforestation, improper land use and climate changes. These are particularly pronounced in regions with high population density and rapid development
Volcanic slope stability in Japan
Japan, located in a seismically active region has experience volcanic eruptions leading to landslides. Human activities including construction on volcanic slopes and influence the stability of these areas. Mount Ontake’s eruption in 2014 is where volcanic activity triggered landslides
Facts about Ponzano Italy 2017
$32000 GDP per capita
2% living in poverty
99% have access to clean water
83 life expectancy
99% literate
4.2 doctors per 1000
Moved about 1 metre per day for 2 weeks
12th February
Reasons for the Ponzano Italy landslide
Volume of 7 metres per metre cubed was triggered by:
The saturation of the slope after the direct and slow infiltration of water related to 2 metres of snow melting due to the increase of temperature between January and February
Intense rainfall from the 6th to 10th of February of 81 mm which was 93% of the total
Social impacts on Ponzano Italy
Over 100 evacuated from 35 houses
Several buildings collapsed or sustained severe damage
Evacuated residents staying at hotels or with friends and family
Losses minimised due to slow nature
Economic impacts on Ponzano Italy
Limited due to small population
Losses to 35 properties
Environmental impacts on Ponzano Italy
Agricultural areas surrounding deemed unsafe due to possible further movement
Political impacts on Ponzano Italy
Civitella del Tronto town hall said it wasn’t possible to stop the landslide and damaged houses are not fit to use
Civil Protection Department and National Research Council set monitors to track movement and firefighters recover belongings
Local health authority sent psychologists to assist
Facts about Freetown Sierra Leone 2017
$500 GDP per capita
60% in poverty
50% have access to clean water
52 life expectancy
48% literate
0.05 doctors per 1000
Rapid onset after 3 days of heavy rainfall
14th of August
Location of Freetown landslide
Freetown is a major port on the Atlantic and is in the West. Is Sierra Leone’s major urban, economic, financial, cultural, educational and political centre as is the sea of government. Population was 1055964 in 2015. Has thick wood and partly deforested mountains. Construction of large homes in hills and unrestricted deforestation for residential areas weakened stability of nearby slopes and caused soil erosion
Reasons for the Freetown landslide
Factors include regional topography and climate with elevation close to sea level and position within a tropical monsoon climate. Poor infrastructure and loss of protective natural drainage systems. Unorganized settlements and municipal works on floodplains so narrow water passages. During floods, drains are blocked by waste especially in poor communities so higher surface runoff. 104 cm of rain from July to mudslide (x3 average)
Social impacts on freetown
1141 dead or missing
Hundreds of homes damaged
3000 left homeless and moved to emergency camps
Accessibility between communities lost due to cutting of communication
Unsanitary waters fear cholera but aid provided storage tanks, tablets and hygiene courses
Economic impacts on Freetown
Roads, bridges and footpaths blocked or washed away ($1m in damages)
Power outages due to fear of electrical accidents
Water shortages so UNICEF distributed 26000L each day
Environmental impacts on Freetown
Loss of agricultural productivity
Loss of biodiversity
Changes to surrounding river drainage patterns
Sedimentation of rivers and streams and pollution of surface water by mud and sewage
Political impacts on Freetown
President Ernest Bai Koroma did a national broadcast on August 15th declaring a state of emergency and announcing a relief centre in Regent
Aid from China, UK, Spain, Ireland, Israel. WFP provided rations for 7500. EU authorised 300000 euros in humanitarian aid
Causes of Abbotsford landslide
Displacement of 50m in 30 minutes leaving a rift 30m deep. It was a block slide of sandstone resting on a bed of weaker clay. The slope was 7 degrees. Water collected in the impermeable clay, reduced its strength and cohesion and caused the sandstone to slope along the boundary. 54 metres per metre cubed of material. Started as a slow creep and became rapid with speeds of 1.7m mer minute. Lasted 30 minutes. 18 hectares affected. Deforestation had reduced evapotranspiration and less binding of soil by plant roots. Urbanisation in previous 40 years modified slopes by cutting and infilling and altered surface drainage. Quarrying of material in 1960’s and 70’s removed base support. Trigger was leaking water pipes and heavy rain
Impacts of Abbotsford landslide
On August 8th a 7 hectare section went downhill at 3 metres per minute with houses and 17 people. 69 homes destroyed or damaged and 200 were displaced. Total cost was over 7 million pounds. Insurance scheme and government relief meant that many were compensated for their loss. Depressed house prices in surrounding areas, psychological trauma and long public enquiry costs were not immediately appreciated
Lessons from Abbotsford landslide
Dangerous landslides can occur on gentle slopes
Attention to early warning can help preparedness and reduce loss of life
Human activity can destabilise slopes
Low frequency, high magnitude events may be hard to predict but mapping and dating of old hazards indicate risks. A regional landslide hazard assessment should be made when there was previous activity
A landslide insurance scheme eased the event cost but money was only available after the event and insurance only covered houses not land
