Natural hazards
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Transcript of Natural hazards
NATURAL HAZARDS
William M. ShehataSaudi Geological Survey
Definition
Natural hazards are naturally occurring physical phenomena having atmospheric, geologic or hydrologic origin.
Natural hazards are not entirely natural for people are also agents of disaster.
Examples of Atmospheric Hazards
Hurricanes Tornadoes Drought Winter storms Dust storms
Examples of Geologic Hazards
Earthquakes Volcanic eruptions Landslides Subsidence
Examples of Hydrologic Hazards
Floods Tsunamis
Geological Hazardsin Saudi Arabia
Landslides, rock falls & debris flows.
Floods. Collapsible & swelling
soil. Sabkha soil. Volcanic hazards.
Dune migration & sand drifting.
Sinkholes & caves. Salt domes. Earth fissures. Earthquakes.
RE
D
SEA
ARABIAN
GULF
ARABIAN
SHIELD
ARABIAN
SHELF
Alwajh
Yanbu
Rabigh
Jeddah
Al-Lith
Tabuk
Hail
Ar-Riyadh
Jazan
Dhahran
Almadinah
42 54
28
20
Scale0 100 200
km
Great Nufud
Ad-Dahna
Elrub-Elkhali
17
Shield and Arabian Shelf
Sabkha
Loess & swelling soilEscarpmentMain valley courseSand sea
Volcanic area (Harrat)
Sinkhole or caves
Al-Jafu
rah
Salt domeEarth Fissures
Landslides, Rock Falls & Debris Flows
Landslides, Rock Falls & Debris Flow
Example of a slow failures
Landslide in California
Example of fast failures
Rock Fall Al Hada road
Al Hada road
Al Baha descend
Jabal Khandamah
Examples of debris flow
Al Baha Descent Bridge #8A failure
Rock Falls
Wedge failure at Al Jowah descent
Wedge failure at the road to Al Soda
Flood Hazards
Flood Hazards
Foods in Wadi
Bayish
Fatiha 1 (hr)
0
2
4
6
8
10
0 2 4 6 8 10 12 14 16 18 20 22 24 26
t (hr)
qp
(m
3 /s)
Sheet flood (Wadi Al Lith)
Collapsible & Swelling Soil
Collapsible & Swelling Soil
Swelling shale of Ra’an formation
(Tabuk)
Crystallization of salt in the shale
(Tabuk)5 cm
Gypsum crystallization
Heave in the shale bed
Collapse in a loess sample
Sabkha Soil
Sabkha Soil
Salt concentrations in sabkha
Sabkha Properties*
* Modified after Hodgson et al. (1985) & Dhowian et al. (1987)
Layer Average Thickness
(m)
Description SPT
(Soil class)
Crust 1.0-1.5 Fine sand-silt cemented with salts
9-16
(ML-SM)Compressible zone
8.0-10.0 Non plastic fine sand to highly plastic organic clay
1-6
(SM, CL, SC, OH)
Base ? Dense to very dense fine sand
Variable up to refusal
Corrosivity*
Sulfates Chlorides
Soil (%) 0.12 – 14.90 0.12 – 10.72
Groundwater (ppm)
1,098 – 3,876 14,200 – 97,625
*Sabkha soil and groundwater can generally be classified as very corrosive (Hodgson et al., 1985)
Effect of sabkha brines on structures
Volcanic Hazards
Volcanic Hazards
Fumarole
Volcanic vent
Harrat Al Madinah
Preliminary studies show an increase in the recurrence rate of volcanic activity in the past 3 million years.
The latest eruption in Harrat Al Madinah was in year 654 H. (1256 G.).
Dune Migration & Sand Drifting
Great Nufud
Elrub-Elkhali
Dune Migration and Sand Drifting
Dune migration
2 Years of Monitoring
Sand drifting erosion & deposition (Eastern Province)
Sinkholes & Caves
Sinkholes & Caves
Collapse sinkhole
(As Somman Plateau)
Collapse Sinkholes
(Al Khobar)
Cover Collapse Sinkholes
(Tabarjal)
Salt Domes
Jazan Salt Dome
Jazan 50 years ago
Jazan now
Salt dome 4 sq. km and 50 m
high
Salt mushrooms
Salt diapiric intrusion
Jazan salt dome
Salt dissolution leads to soil collapse
Rock Salt
EolianDeposits
MixedMaterial
SandstoneGypsum
Cavity
Beach sand
Eolian deposits
Cap rock
Sabkha
N
500 m
Damagedbuildings
Locations of affected buildings
(Modified after Erol, 1989)
Examples of affected buildings
Earth Fissures
Earth Fissures
Earth fissures due to groundwater withdrawal
(Tabah)
Earth fissures due to groundwater withdrawal
(Al Yutamah)
Earth fissures due to 1995 earthquake
(Haql)
Earth fissure associated with Red
Sea tectonics
(Jeddah).
(Al Quhtani, 1998)
Earthquakes
Earthquake Hazards
Earthquake Epicenters
Haql 1995 Earthquake
0 20 40 60
20
40
60
80
0
SPT (Blows/ft)
De
pth
(ft
)
Liquefactionvery unlikely
Liq
uef
acti
on
ver
y lik
ely
Liq
uef
acti
on
dep
end
s o
n s
oil
typ
e &
ear
thq
uak
e m
agn
itu
de
Maximum ground surface acceleration = 0.25 g
Groundwater level
0 20 40 60
20
40
60
80
0
SPT (Blows/ft)D
epth
(ft
)
Liquefactionvery unlikely
Liq
uef
acti
on
ver
y lik
ely
Liq
uef
acti
on
dep
end
s o
n s
oil
typ
e &
ear
thq
uak
e m
agn
itu
de
Maximum ground surface acceleration = 0.15 g
Groundwater level
Liquefaction Potential of Sabkha Soil
Hazard Mitigation
Any action taken to reduce or eliminate the long term risk to human life and property from natural hazards– Understanding of the geodynamic phenomena– Worldwide spread of scientific knowledge– Adoption of appropriate public and management
policies– Increase of awareness programs– Landuse restrictions– Adequate building construction– Wise environmental management
Role of theSaudi Geological Survey
Towards Hazard Mitigation
Define, analyze and recommend remedial measures through its rapid response teams and in-house projects.
Prepare comprehensive and analytical engineering geological maps for the major cities in the Kingdom
Natural Seismograph