DRRR

• Landslides


  Masses of rock, earth, or debris move down a slope. Debris flows, also known as mudslides, are a common type of fast-moving landslide that tends to flow in channels.
• Types of landslide movement

  • Falls
  • Topples
  • Slides (rotational and translational)
  • Flows
• Falls


  • Involve the collapse of material from a cliff or steep slope. Usually involve a mixture of free fall through the air, bouncing or rolling. Results in the collection of rock or debris near the base of a slope.
• Topples


  • Movements of rock, debris, or earth masses by forward rotation about a pivot point. Topple failures involve the forward rotation and movement of mass of rock, earth, or debris out of a slope. Often results in the formation of a talus cone at the base of the slope.
• Slides


  • A downslope movement of material that occurs along a distinctive rupture or slip surface. The slip surface tends to be deeper than that of other landslide types and not structurally controlled. Characterized by a prominent main scarp and back-tilted bench or block at the top, with limited internal deformation. Movement is more or less rotational about an axis.
• Rotational slides


  • Occur on curved slip surfaces where the upper surface of the displaced material may tilt backwards toward the scarp.
• Translational slides


  • A downslope movement of material that occurs along a distinctive planar surface of weakness such as a fault, joint or bedding plane. Some of the largest and most damaging landslides on Earth are translational. They can be very rapid where discontinuities are steep.
• Flows

  • Landslides that involve the movement of material down a slope in the form of a fluid. Often leave behind a distinctive, upside-down funnel shaped deposit where the landslide material has stopped moving. Types include mud flows and debris flows.
• Landslide materials


  • Soil
  • Debris
  • Rock
  • Garbage
• Landslide triggers


  • Natural triggers: intense rainfall, weathering of rocks, ground vibrations created during earthquakes, volcanic activity
  • Man-made triggers
• Landslide triggering conditions


  • Steep slopes
  • Weakening of slope material
  • Weathering of rocks
  • Overloading on the slope
• Common signs of impending landslides

  • Tension cracks
  • Fractured rocks and sediments
  • Sliding slope and active slides
  • Soil overburden
• Measures to minimize landslide risks

  • Hazard mapping
  • Public information
  • Engineering intervention
• Techniques for landslide treatment

  • Land use improvement: conservation plantation, grass plantation, on-farm conservation, agro-forestry, safe water drainage, runoff harvesting ponds or dams
  • Drainage management: surface and subsurface drainage
  • Surface erosion control: grass/tree planting, jute netting, mulching, wattling, brush layering
  • Erosion control in rills: fascine, contour grass planting, rip-rap
  • Erosion control in gullies: palisade, check dams
  • Slope failure due to slope cutting or steep slope: crib walls, retaining/toe walls
  • Slope failure due to heavy load on slope: excavation, filling rock at toe
• Research and field studies indicate that vetiver grass significantly helps reduce landslides and soil erosion and also improves crop yields.
• Sinkholes


  Holes in the ground that form when water dissolves surface rock, often limestone which is easily eroded by water movement.
• Different techniques can address the various problems in landslides.
• Thunderstorm life cycle


  1. Developing stage: cumulus cloud pushed upward by rising air, little to no rain and occasional lightning

  2. Mature stage: updraft continues to feed the storm, precipitation begins to fall creating a downdraft

  3. Dissipation stage: large precipitation overcomes the updraft, downdraft cuts off warm moist air, rainfall decreases but lightning remains a danger

  
• If a storm isn't spinning, it can't be a tropical cyclone

  
• A tropical cyclone will always have a name

  
• A tropical cyclone cannot form over land

  
• The name for hot air rising is 'convection'
• A tropical cyclone will have winds of at least 74mph

  
• A tropical cyclone can form over water that is less than 20°C

  
• A tropical cyclone would spin counterclockwise in the North Atlantic
• A tropical cyclone could not form in the Arctic Ocean

  
• A tropical cyclone near Japan would be called a typhoon, not a hurricane

  
• Tropical cyclones can happen in any month of the year
• Key impacts of tropical cyclones

  • Storm surge: rise in sea level due to low pressure and onshore winds
  • Extreme rainfall: over 6m recorded in some cases
  • High winds: up to 165mph recorded

  
• Cycle of a thunderstorm

  1. Developing stage

  2. Mature stage

  3. Dissipating stage
• Developing stage


  • Cumulus cloud being pushed upward by rising column of air (updraft)
  • Towering cumulus cloud
  • Little to no rain but occasional lightning

  
• Mature stage


  • Updraft continues to feed the storm, but precipitation begins to fall out of the storm, creating a downdraft
• Dissipation stage


  • Large amount of precipitation produced, updraft overcome by downdraft
  • Gust front moves out, cuts off warm moist air feeding the storm
  • Rainfall decreases but lightning remains a danger

  
• Wind threat levels


  • 39-61 km/h
  • 62-88 km/h
  • 89-117 km/h
  • 118-184 km/h
  • 185 km/h or higher

  
• Wind threat: 39-61 km/h

  22-33 kt, 10.8-17.1 m/s

  
• Wind threat: 62-88 km/h


  34-47 kt, 17.2-24.4 m/s

  
• Wind threat: 89-117 km/h


  48-63 kt, 24.5-32.6 m/s

  
• Wind threat: 118-184 km/h


  64-99 kt, 32.7-51.2 m/s

  
• Wind threat: 185 km/h or higher


  100 kt or higher, 51.3 m/s or higher

  
• Warning lead time


  36 hours for 39-61 km/h

  24 hours for 62-88 km/h

  18 hours for 89-117 km/h

  12 hours for 118-184 km/h and 185 km/h or higher