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Overview

Geological hazards are natural phenomena that cause major problems all over the world. The expansion and development of cities leads to an increase in impact and damage due to geological hazards.  In general, most of the geological hazards associated with desert environments are related to natural conditions, although some may be due to human activities. Potential geological hazards that might occur under desert conditions include erosion and deposition associated with sand drifting and dune movement, corrosion, low bearing capacity of sediments, sabkha zones that are unsuitable for construction, land subsidence due to loose soil, salt domes, rock falls, landslides, earth fissures and sinkholes, subsidence, flash floods, and many more.

 
Objectives

In order to serve the community, the Geological Hazards Team of the Saudi Geological Survey started a program to study and monitor geological hazards, whether natural or man-made, throughout the Kingdom of Saudi Arabia. The teams evaluate the different geological hazards, predict their origin and mode of formation and calculate the risk from these hazards on lives and property, as well as on the surrounding environment. Many technical reports have been published by the Department on flooding and other geohazards in the Kingdom. The locations of geological hazards in Saudi Arabia are shown in the map below.
 
Generalized geohazard map for the Kingdom of Saudi Arabia.
 
Examples of Geological Hazards

Some examples of geological hazards that have been investigated and documented by the Geological Hazards Department are as follows:

1. Flood Hazards

Although the average rainfall in the coastal areas of the Kingdom is very small, rainstorms on the nearby mountains can generate flash floods that damage properties and result in loss of life. The Geological Hazards Team has investigated several wadis between Jizan and Jeddah and is continuing studies of other wadis.
The aim is to prepare detailed hydrological studies of the wadis in order to determine the potential danger from the floods and to recommend suitable remedial measures.
 
Damage due to flash floods that occurred in Jeddah in November 2009.
 
2. Rock Fall Hazards

Landslides are rock, earth, or debris flows on slopes due to gravity. They can occur on any terrain given the right conditions of soil, moisture, and the angle of slope. Integral to the natural process of the earth's surface geology, landslides serve to redistribute soil and sediments in a process that can be in abrupt collapses or in slow gradual slides. Also known as mud flows, debris flows, earth failures, and slope failures, they can be triggered by rain, floods, earthquakes, and other natural causes as well as human-made causes, such as grading, terrain cutting and filling, excessive development, and so on. The factors affecting landslides can be geological or by man-made, and can occur in developed or undeveloped areas, or in areas where the terrain has been altered for roads, houses, utilities, buildings and mining activities.
 
The Saudi Geological Survey is studying landslides in order to mitigate the risks. Landslides may be more devastating than all other natural hazards combined, and can affect utilities, transportation, and public and private infrastructure. Most of the rock slopes along the descents between the Arabian Shield mountains and the Red Sea coast that cut through the escarpment are subject to slope instability and rock falls, especially after rain storms.
 
Rock falls close roads and damage infrastructure.
 
3. Karst Hazards

Different types of sinkholes have been recognized in Saudi Arabia. The sinkholes are of various sizes, shapes and occur at different depths. Their presence may cause a direct risk to infrastructure such as urban areas, roads, areas being developed, and farmland. Some sinkholes have also appeared in barren uninhabited areas. In recent years more than eight large sinkholes or ground collapses have occurred to the west of Al Khafji and in the An Nu’ayriyah area (northeast Saudi Arabia) due to dissolution of the underlying limestone. 
 
 Property damage due to a collapsed sinkhole.
 
4. Earth Fissures
 
Earth fissures can result from several geodynamic processes. Earthquakes can form fissures as was the case along the coast to the south of Haql in 1995. Earth fissures can also be formed due to excessive groundwater withdrawal, as occurred at Tabah, An Naiy and Al Yutamah. The Geohazards and Engineering Geology Teams are monitoring the movement across earth fissures and producing hazard zonation maps.
 
Open earth fissure.
 
 
5. Problematic Soils and Rocks
Some problematic soils and rocks may pose a danger to anything constructed on them.  Soils such as sabkha may collapse and react with foundations while loess can also collapse.  Clayey soils and weak rocks such as claystone and shale may swell.  The Geohazards and Engineering Geology Teams are investigating the sabkha soils in Jeddah, Jazan, Yanbu and Al Jubail and swelling rocks at Al Qasim.

5-1. Sabkha Hazards
Sabkha in general forms due to variations in the rate of evaporation of salt water in the soil.  Engineers classify sabkha into four common types: 1) Sabkha, 2) Playa, 3) Salt Playa, and 4) Saline. After the evaporation of saline water from a lake a crust of salt is formed. Coastal sabkha is formed from continental sediments that are mixed with sea water during regression of the sea level. The mineral composition of coastal sabkha is characterized by the presence of aragonite, calcite, gypsum, and dolomite. These sabkha soils have a negative impact on infrastructure causing problems in buildings. The degree of damage depends on the characteristics of the sabkha, the degree of subsidence, and the bearing capacity of the sabkha. A technical report about the characteristics of the Jizan sabkha has been produced by the Department.
 
a) Subsidence and tension cracks in an asphalt area;
b) Sinkhole in front of a building. 
 
5-2. Loess Soil
 
Loess soil is an unconsolidated well-sorted clastic deposit. It is relatively homogeneous, seemingly non-stratified, and extremely porous. Loess has different definitions, but is generally considered to be wind-blown (aeolian) silt where the sediments were transported by wind. Loess soil mainly consists of quartz, feldspar and mica grains that are angular showing little polishing or rounding. Because the grains are angular, loess often retains the shape of banks for many years without slumping. The soil characteristic called vertical cleavage allows the formation of cave dwellings. Loess may be readily eroded by water, wind and seismic activity. Loess soil occurs in various areas in the Kingdom such as in Jizan city.
 
a) The distribution of loess soil and new urban infrastructure to the east of Jizan city;
b) the appearance of Loess soil in the Jizan area.
 
 
5-3.  Sand Dunes
 
Drifting sand and dune movement are some of the most serious natural problems facing the Arabian Peninsula due to the expansion of cities, roads, industries, and agricultural development.  If not controlled, movement of sand dunes creates problems for industrial plants, residential areas, roads, power lines, and pipelines. Problems that have been studied within active dunes include closing of roads, as well as other problems that affect the development of various areas.
 
5-4. Salt Domes
 
Problems related to salt domes occur in many locations in the Jizan area, especially in the old city of Jizan.  Lenses of salt extend away from the salt domes at depths that range from a few meters to tens of meters under the flat areas.  These cause problems that include damage to buildings and infrastructure or even collapses, with building failures, fractures, and tilting, road cracks, an undulating ground surface, and tilting of posts and electricity poles.