DRRR

• A sinkhole can be described as the downward movement of earth’s crust towards its gravity. It is the sinking of the ground surface above an underground void or depression. Sinkholes could be due to the collapse of an old mine or cave, and deterioration or compaction of soils and construction materials used for filling (Pittsburgh Geological Society).
• The United States Geological Survey (USGS) defined ground subsidence as the loss of surface elevation due to the removal of subsurface support. There are diverse forms of ground failure or subsidence, many are small and local in nature, while others are broad and can affect a wider area of concern.
• Ground subsidence has resulted from natural causes, such as tectonic motion and sea level

  rise. Ground subsidence can also come from man-induced causes such as the heavy

  withdrawal of groundwater and geothermal fluids, oil, and gas; other mining activities such as

  extraction of coal, sulfur, gold, and other solids; and underground construction (tunneling).
• Formation of Sinkholes

  
  

  Sinkholes form in areas that geologists call karst terrains. Areas that are described as karst terrain have bedrocks that are typically made up of limestone, dolomite, or gypsum. Those types of rocks can be dissolved by groundwater over time. The type of bedrock in karst terrains result in features like springs, caves, and sinkholes.
• When acidic water (from soil and air) enters a karst terrain, it easily penetrates the area and creates horizontal and vertical cracks and crevices that lead to the development of a conduit system. A conduit or an underground river forms from the pathways created by penetrating acidic water. Because of this, underground erosion and formation of underground caves may lead to the development of sinkholes.
• Types of sinkholes

  
  

  Dissolution sinkholes

  Dissolution can be described as the process of dissolving of rocks,

  often by water or acid. This type of sinkhole forms from dissolution

  of the limestone or dolomite. Dissolution happens intensively where

  water first comes in contact with the rock surface. It can also occur

  where water passes through pre-existing openings, crevices or

  fractures in rocks.
• Cover-subsidence sinkholes

  
  

  In areas where the covering sediments contain sand and are

  permeable, cover-subsidence sinkholes can eventually develop. In

  areas where the covering sediments contain more clay,

  cover-subsidence sinkholes may still develop but may be undetected for longer periods of time.
• Cover-collapse sinkholes

  
  

  Cover-collapse sinkholes occur where the covering sediments

  contain a significant amount of clay. These sinkholes may develop

  abruptly (over a period of hours) and cause catastrophic damages.

  Over time, surface drainage, erosion, and deposition of sinkhole will

  develop into a shallower bowl-shaped depression.
• Human-induced sinkholes

  
  

  Some sinkholes are associated with human activities like

  groundwater pumping, construction, and land development

  practices. Sinkholes can also form when water diversion systems are

  developed for human activities. When the land is changed due to

  industrial activities, the weight of new materials placed on the

  surface can cause the collapse of the supporting material

  underground, causing a sinkhole.
• Some Causes of Ground Subsidence

  
  

  Ground subsidence can be a result of natural processes or as effects of human activities. Aside from dissolution and diversion of natural water drainage patterns, dewatering or overdraining of organic soil and peat can shrink the materials causing the ground to subside.
• Compaction of soil due to natural or man-induced processes will displace air spaces, making the soil impenetrable and more susceptible to subsidence. Subterranean mining or underground mining activities including extraction of fluid minerals displaces numerous materials under the surface. A possible effect of climate change, thawing permafrost erodes not only water but other solid materials that are part of its composition. Thawing permafrost shrinks the land and affects human and natural installations above its surface.
• Effects of Ground Subsidence

  
  

  Ground subsidence can impact agricultural lands, industrial processes, and infrastructure. Farm lands, irrigation systems, and groundwater wells can be damaged or destroyed. Infrastructures that are on subsiding ground can also be damaged or destroyed. Mining areas tunnels and surrounding areas can collapse. Moreover, sudden subsidence can cause injuries and fatalities.
• Some Tips to Reduce Occurrence of Ground Subsidence

  
  

  ● finding alternative sources to groundwater;

  ● avoiding building infrastructure in certain distances near land fissures;

  ● routing drainage away from fissures; and

  ● prohibiting residential zones in or near fissure areas or types of ground that have high

  subsidence susceptibility.
• Major Types of Landslides

  Fall: A fall begins when the material on cliffs or steep slopes lose support or becomes fractured from the main rock. The materials which can be rock and soil of different sizessubsequently descend by falling, bouncing, or rolling; until they reach lower or flatter surfaces.
• Topple: A topple happens when a block of material is detached from a steep slope such as a cliff, and moves forward and downward around a point of axis (imagine a rotating motion). Toppling can occur because of the weight of the material or due to the cracks in the mass created by water or ice. Some topples can also end up as falls or slides.
• Slide: A slide occurs when the detached mass of materials such as rocks, soil, and sometimes organic matter move along a downward sloping surface. The volume of material increases as the mass moves downwards away from its origin. When the displaced mass is moving along a concave surface, it is called a rotational landslide or slump. Otherwise, when the mass that slides down and outward along a downward sloping surface, it is called a translational landslide.
• Flows: A flow occurs when materials from (usually) gentle slopes are detached and flow like a viscous liquid along a surface.
• ● Debris Flow: This is a rapid movement of slurry that is informally called mudslide is formed from water that combines materials such as rocks and soil and sometimes organic matter. Lahar flow is also known as volcanic mudflow. Lahar flows originate on the slopes of volcanoes and are a type of debris flow. Lahar mobilizes the loose accumulations of tephra (the airborne solids erupted from the volcano) and related

  debris.
• ● Debris avalanche: This occurs from sudden collapse of unstable slopes and the fragmented debris rapidly moves downwards along the slope. In some cases, snow and ice will contribute to the movement and if a significant amount of water is present, it can become a debris flow.
• ● Earth Flow: When the flow has a high amount of silt or clay, the flow becomes a more viscous earth flow. Earth flows can range from very slow and almost imperceptible creep to rapid and catastrophic.
• Spreads: This occurs when the mass of soil or rocks extends or spread laterally. This mass movement of rocks and soil can usually be observed when there is liquefaction or an earthquake.
• Factors that Influence Landslide Development

  
  

  Geological factors that influence landslide include properties of rock and soil that renders them weak or sensitive to movement. For instance, weathered and fractured materials are susceptible to landslide as they are the ones that will be most easily detached from the main material. Permeability and stiffness of materials can also be factors that will make chunks of land susceptible to landslide.
• Morphological factors that influence landslide include the

  shape of land and its slope, tectonic and volcanic activities, erosion and deposition, water, the

  amount of vegetation on the rock and soil surface as well as the boundaries of the land mass

  involved.
• Human factors that affect landslide include development activities that modify the geological and morphological factors of the land. Mining, excavation, building of roads and dams, irrigation, and deforestation are some of the human activities that increase the susceptibility of areas to landslides.
• Causes of Rainfall-Induced Landslides

  The three main natural causes of landslide are water (rainfall), seismic, and volcanic activity.
• Coastal erosion involves the breakdown and removal of materials from the coastline due to wave action, tidal currents, and human activities. Coastal erosion is not just a concern in the Philippines, but it is also a global issue because 15 square-kilometers of shores are retreating annually due to sea level rising and global warming.
• Coastal erosion can be classified either as natural or anthropogenic, temporary or long-term.

  Temporary erosion is reversed by a period of accretion.
• Types of Coastal Erosion

  
  

  Mechanical Erosion of Waves: The mechanical action of waves is the main erosion factor in coastal environment, through high energy waves or storms waves. In low energy conditions, the erosive action of waves is reduced; however, they still contribute significantly to the removal of weathered material. Apart from removing loose material through waves, two main results are the abrasion of rock surfaces and the pressure fluctuations induced on rocks by the waves.
• Weathering: Coastal cliffs and intertidal coastal platforms are exposed to alternating wetting and drying of salt spray, wave swash, tides, and rain. Subsequently, they constitute suitable environment for many physical and chemical processes of weathering.
• Bioerosion: Bioerosion is the removal of rocks and minerals through the actions of organisms. The rocks and sediments in tropical regions are more susceptible to coastal erosion, due to the large biodiversity in its marine ecosystems. Marine organisms use rocks for shelter and even as a source of their own materials. For instance, limestone substrates are involved in the biochemical and biophysical processes in corals and shelled animals.
• A huge factor that influences the rate of bioerosion is the spatial distribution of marine organisms along the rock surface, which is largely controlled by the available moisture that largely depends on tidal currents and wave action.
• Mass movements: The steep slopes of rocky shores are unstable and are prone to mass movements depending on the properties and structure of its rock composition.
• Factors that Influence Coastal Erosion

  Coastal erosion is a process that is affected by natural and man-made factors.

  • Climate: Climate defines the weather conditions of an area and affects physical phenomena of coastal zones such as waves, underwater currents, and storm surges. Wind regime is related to wind waves and coastal currents. The stronger the wind, the higher the wave height. Higher waves bring more erosive actions.
• • Lithology of rocks: The hardness of the rock, its resistance to subaerial and marine erosion affect its susceptibility or resistance to weathering and erosion. A rock’s exposure to wave activities can result to the removal of base materials from the shores.
• • Global sea level rise: It is a natural phenomenon but can be amplified by human-induced global warming due to human development activities that contribute to making the faster warming of the earth. Global warming affects the rise in sea level and contributes to the thermal expansion of ocean water, and ice sheet melting in the Polar Regions. This unprecedented sea level rise poses a threat to coastal communities and countries around the world. The main three effects of this factor are coastal erosion, flooding of wetlands, and salt contamination of coastal aquifers.
• • Man-made interventions: Coastal areas are a strategic location for human activities. They can be used for military bases, recreational spaces, tourist destinations, and a real estate prime land. Due to these, coastal areas become vulnerable to the effects of these human developments. Another noteworthy human activity is sand extraction that is harmful to coastal areas and its inhabitants.
• Bolide Impact

  
  

  Near-Earth objects (NEOs) are used to define the rocky or metallic asteroids and icy comets found between Jupiter and Mars. These near-earth objects were made from the same materials that made up the planet in the solar system, planetesimals.
• These materials attract each other, but there are two results from this attraction, the formation of planets and destruction, that make up clouds of fragments. The area where these fragments are located is called the asteroid belt, and these fragments are orbiting the sun. Due to some disturbances, these near-earth objects, also called Mars-crossers, can move directly to the inner solar system and could hit or impact one of the inner planets. Simply speaking, these objects may hit the earth.
• Bolide is a generic term used to define any celestial bodies entering the earth surface, creating a fireball. Superbolide is the term used to describe a relatively larger bolide. Once a bolide hits the earth, it could explode upon impact or create a crater formation. Bolide impact depends on the features of the foreign body that enters the earth, like its size, composition, density, and its ability to survive its entry to Earth.
• Superbolides can have cratering formation impacts. In natural history, superbolides increased the incidence of climate change and sea level change. Intense tectonic activities, earthquakes, and increased volcanism are also linked to bolide impacts. These environmental impacts of bolides can trigger global mass extinction and global environmental dangers.