Lesson 3: Geological Hazards

1.RAINFALL-INDUCED LANDSLIDE
2.SINKHOLE

• geological hazards in the Philippines

RAINFALL-INDUCED LANDSLIDE

• Rainfall-induced landslides happen when heavy rain weakens slopes, making land unstable.

• Tectonic activity can make some areas more prone to landslides, with rain worsening the soil’s stability.

• Mountainous regions and areas with heavy rainfall are most susceptible to landslides.

1.THE SLOPE
2.SOIL TYPE

• Apart from the rain, there are two major geological factors that scientists consider:

1.STEEP SLOPES
2.WEAKENING OF SLOE MATERIALS
3.WEATHERING OF ROCKS
4.OVERLOADING ON THE SLOPE

• According to the country’s data in 2018, landslides essentially occur due to

FAILURE

• when a land falls

1.FALLING
2.TOPPLING
3.SLIDING
4.SPREADING
5. FLOWING

• There are five common modes of failure of landslides.

FALLING

• rocks or soil suddenly drop or fall freely from a steep slope or cliff. this happens when gravity pulls loose material down

TOPPLING

• columns or blocks of rock tilt or move forward and fall over, like toppling dominoes. this is caused by steep fracture or joints in the rock leaning outward.

SLIDING

• amass of soil or rock moves down a slope along a defined surface, like a smooth place or curve. the material slides as one block or in pieces

SPREADING

• the ground at the base of a slope spread outward, causing the material above it to crack and move down slowly. This is common where soft soil lies under firmer ground

FLOWING

• soil, mud, or debris becomes saturated with water and flows downhill like a thick liquid, often rapidly and unpredictably 

• Springs, seeps, or saturated ground are present in areas that have not typically been wet before.

• There are new cracks or unusual bulges in the ground, street pavements, or sidewalks.

• The soil is moving away from foundations.

• Ancillary structures such as decks and patios are tilting and/or moving relative to the main house.

• Tilting and/or cracking of concrete floors and foundations are observed.

• Water lines and other underground utilities are broken.

• Telephone poles, trees, retaining walls, or fences are leaning.

• Sunken or down-dropped roadbeds are seen.

• There is a rapid increase in creek water levels, possibly accompanied by increased turbidity (soil content).

• Offset fence lines are visible.

• There is a sudden decrease in creek water levels even though rain is still falling or just recently stopped.

• Sticking doors and windows, and visible open spaces indicate that jambs and frames are out of plumb.

• A faint rumbling sound that increases in volume is noticeable as the landslide nears.

• Unusual sounds, such as trees cracking or boulders knocking together, might indicate moving debris.

• Signs of Impending Rainfall-Induced Landslides

SINKHOLE

• according to the usgs (2018), is an area of ground that has no natural external surface drainage; hence, when water dissolves surface rock, a hole is formed

1.DISSOLUTION
2.SUFFUSION

• are two processes that creates sinkholes,

DISSOLUTION

• water with carbon dioxide creates a weak acid (carbonic acid) that slowly dissolved rocks like limestone and dolomite underground

SUFFUSION

• sediments above underground cavities slowly fall in through cracks, making cavities larger and causing the land above to sink

• Circular or round depressions or dips in the ground surface.

• Localized sinking or subsidence anywhere on the land.

• New cracks appearing in the ground, sidewalks, or streets.

• Cracks in the foundation, walls, or floors of buildings.

• Doors and windows that become difficult to open or close properly.

• Tilting or leaning trees, fence posts, or utility poles.

• Bare or dead patches of grass or plants, often in circular shapes.

• Unusual pooling of water or the sudden appearance of small ponds after rain.

• Visible exposure of buried objects like tree roots or fence posts.

• Sudden drainage or disappearance of water from ponds or lakes near the area.

• Signs of Impending Sinkholes