EOSC 114 Unit 3 Landslides.docx

3 Pages
163 Views
Unlock Document

Department
Earth and Ocean Sciences
Course
EOSC 114
Professor
Leah May Ver
Semester
Fall

Description
Unit 3: Landslides  Explain how the impact of landslides depends on 1) population density, 2) economic infrastructure, and 3) population preparedness. o As population density increases, increasing damage. o Most fatalities from a slides are under-reported as they accompany major disasters  Japan has the most deaths from landslides per year, but highest pop density as well o Largest landslides in Canada happen on West coast (here), between BC and Alberta and in Quebec + Ontario  Explain why British Columbia has the highest frequency of landslides in Canada and what we should expect as our population expands into the mountains. o Mountainous terrain, lots of rain, complex geology (unconsolidated glacial sediments) and many possible triggers  South BC: return period is 25 – 70 years for large slides  Distinguish between the 3 main failure modes (falls, flows, and slides) and how they are influenced by geology. o Falls: very fast.  Occur on very steep slopes (usually rock)  Material detaches because of weakness – falls very fast due to gravity o Slides – cohesive block moves on a surface  Vary from slow to fast. Usually soil, rock or debris  Curved/bowl shaped surface: Rotational slide (slump)  Usually weak material (sediment). Characterized by scarp above slide.  Flat/planar surface: Translational slide  Usually strong material. Cohesive block slides down. o Flows – fluid motion (Chaotic)  Very fast – mudflows can be up to 80 km/h  Soil, mud, wet debris, rock. Water usually involved o Complex movements (combination of above)  Categorize, identify, and name a variety of different landslides o Landslides classified mainly by type of material and type of movement. Rate of movement also important.  Materials: Rock, Soil/Earth, Mud, Debris  Define Angle of repose o Steepest angle a slope can maintain without collapsing. Depends on material.  Assess the balance between the strength of the slope and the destabilizing forces acting on it (Factor of Safety) o Stability of a slope depends on  Driving forces: Gravity  Gravity is manifested as Shear stress “T”  Gravity force is parallel to the slope, moving downwards  Resisting forces (Shear strength) – “Tf  Friction – resistance to sliding  Cohesion – material holding together  Normal stress – perpendicular to slope o Factor of Safety (Fs) = (Tf/T) = (Shear strength / Shear Stress) = (Strength / Stress)  FS >> 1, stable slope  FS < 1, unstable – failure may occur  At angle of repose, FoS = 1 or just above.  Compare and contrast landslide causes and landslide triggers. o Causes – usually long term factors that lead to instability of slope  Reduce shear strength of a slope o Triggers – translate instability into motion. Usually short term events. o There can be many causes, but only one trigger.  List and describe several external causes of landslides o Factors outside of slope that affect stability o High slope angle o Undercutting of a slope (removal of bottom) by roads, rivers, buildings o Overloading a slope with excess weight o Vegetation is weird…  R
More Less

Related notes for EOSC 114

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit