The Earth we place is the result of ongoing geological processes of endogenous forces and exogenous forces that can form mountains, valleys, plains, rivers, oceans, lakes, and other beauties. But in addition, not all geological processes produce natural beauty, it can even cause natural hazards caused by geological processes, which can also be called geological disasters.
Based on law (UU no. 24 of 2007), natural disasters are disasters caused by natural events or events such as earthquakes, tsunamis, volcanoes, floods, droughts, typhoons and landslides.
Geographically, Indonesia is a meeting between 3 tectonic plates; namely Eurasian continental plate, Indian Ocean-Australian Plate, and Pacific Plate (Figure 1). Plate tectonic activity that resulted in the formation of a series of volcanoes scattered in Sumatra, Java, Nusa Tenggara, Sulawesi, until Papua. Volcano in Indonesia is part of a series of volcanoes throughout Asia-Pacific which is often referred to as the ring of fire (Figure 2), of course, this volcano can cause eruption / volcano eruption.
Volcanic activity in addition to impact on the eruption of volcano eruption, the sediment is the result of volcanic eruptions in the form of gravel mixture usually do not have a cohesion between components / grains so that on a steep slope will easily occur landslides.
Figure 2. Pasific Ring of Fire (Gringer, 2009; accessed via wikipedia)
The movement of tectonic plates can also trigger earthquakes to stabilize the collision plates, when an earthquake occurs under the sea it will produce tidal waves, if very high tidal wave will cause a tsunami.
Indonesia in tropical climate area which only has 2 seasons, that is rainy season and dry season. Weather change, temperature, wind direction is quite extreme can also cause disasters such as; floods, landslides, droughts, and forest fires.
Disaster management based on law (UU no.24 of 2007) there are 3 phases, include:
Geographically Indonesia lies in a series of fire rings extending along the pacific plate which is the most active tectonic plates in the world. This zone contributes about 90% of earthquake events on earth and almost all of them are the largest earthquakes in the world (Kramer, 1996 in BNPB notes).
II. Sumatera Utara
III. Sumatera Barat – Jambi
VII. Jawa Barat
X. Jawa Timur – Bali
|XI. Nusa Tenggara Barat
XII. Nusa Tenggara Timur
XIII. Kep. Aru
XIV. Sulawesi Selatan
XV. Sulawesi Tenggara
|XVI. Sulawesi Tengah
XVII. Sulawesi Utara
XVIII. Sangihe Talaud
XIX. Maluku Utara
XX. Maluku Selatan
|XXI. Papua Utara
XXV. Kalimantan Timur
Figure 3. Map of earthquake-prone distribution in Indonesia
Earthquakes are vibrations in the earth caused by the release of energy accumulated suddenly in rocks deformed. Earthquakes can be defined as wave propagation in the rock / soil period derived from the release of kinetic energy coming from within the earth. Source of energy released can come from the results of plate collision, volcano eruption, meteor fall, or landslide period of rock / soil. Almost all earthquake events are related to a fracture, which is a stage of rock deformation or tectonic activity and is known as a tectonic earthquake. The spread of epicenter in the world spread along the boundaries of the plate (divergent, convergent, and transform), therefore the occurrence of earthquakes is closely related to plate tectonic theory.
Intensity and magnitude of the earthquake occurring on the earth surface can be known through a seismograph tool, which is a very sensitive seismic vibration recorder placed in various locations on the earth with a unit of the richter scale from 1 to 10. Earthquake waves that propagate during rock, water can cause buildings and roads, drinking water, telephone, electricity and gas to be damaged. The degree of damage is largely determined by the magnitude of magnitude and intensity, with timing and location of the epicenter earthquake.
An earthquake can trigger another disaster will occur, aftershock caused by the earthquake are: soil cracks, vibration / shock ground, ground movement, fires and tidal waves / tsunami.
Generally, earthquakes often affect the fractures and faults of the earth’s surface which is known as the regional deformation of the earth’s crust. Deformation of the earth’s crust can lead to crashed and broken surfaces to a very large area (Figure 4).
Earthquake disasters that are directly felt and have a very serious impact are the collapse of buildings caused by earthquake vibrations / rocks that propagate on rock / soil media (Figure 5). Generally, buildings located above the rock layer of the firm (firm) impact is not too severe when compared with buildings located above saturated sedimentary rocks.
Various types of landslides can generally occur simultaneously with the occurrence of earthquakes. Almost all landslides can occur in a radius of 40 km from the epicenter and for a very large earthquake could reach a radius of 160 km. Basically, earthquake vibration is more as a trigger the occurrence of landslide or ground movement. In this case the earthquake is induced by the movement of the soil, while the landslide and the new soil movement will occur when the interconnection between the granules is weak, saturation of rock / sediment, porosity and high permeability of rock / soil.
The main and frequent damage occurring at the time of the earthquake is fire (Figure 6). Generally the earthquake induces fire from the breaking of power lines, gas, and power plants in operation that eventually cause a fire.
Tsunami is a thrust fault or normal fault in the ocean floor during an underwater earthquake, this condition will cause a very large tidal wave. Tsunami comes from Japanese. “tsu” means port, “nami” means wave so that it is generally interpreted as the great tide of the sea at the harbor. Tsunami is a disaster with the character of fast-onset disaster or type of disaster with a fast process. Tsunamis can occur from near-field locations whose timing is less than 30 minutes from the source to the monitoring coastline and far-field locations where the monitoring time to the monitoring coastal area is longer than 30 minutes or the tsunami source has more distances than 1000 km. The character of the tsunami incident in Indonesia is generally local, where the source of the tsunami is relatively close so it only has a short time to anticipate or evacuate. In addition to earthquakes, active volcanic eruptions can also trigger a tsunami.
Indonesia is an island state that has the longest volcanic arc in the world. Indonesia has 127 active volcanoes, or about 13% of the world’s active volcanoes located in Indonesia (Figure 7), making it the world’s largest volcano owner. Approximately 60% of this amount is volcano which has potentially big hazard for the population that is nearby, so for the sake of safety and survival of society need to be aware of this danger.
|Figure 7. Map of volcano distribution in Indonesia (PVMBG)|
Volcano is a crater or fracture hole in the earth’s crust where the discharge of magma fluid or gas or other liquids to the surface of the earth. Material that erupted to the surface of the earth generally truncated cone shape. Volcano is classified into 4 sources of eruption, among others:
The movement between tectonic plates can cause four different volcanic arcs (Figure 8):
The impact of volcanic eruptions on the environment can be positive and negative impacts. Positive impacts of the activity of a volcano on the environment are mineral industry, geothermal energy, natural resources, tourism area, and water resources. While the negative impact / volcanic eruption hazard, among others: hot clouds, burst material, heavy ash rain, lava flow, lahar flow, poisonous gas, and tsunami.
|Figure 10. Hot clouds of Mt. Semeru (Website: PVMBG)|
Hot clouds are a mixture of eruption material between gas and rocks that are pushed down due to high density and saturated liquid rolled turbulently like cloud mounts along the slopes (Figure 10). The speed of this hot clouds is about 60-145 km/h, high temperatures around 200-800 0C with distances can reach 10 km or more from the eruption center, so it can destroy buildings, uprooting big trees (trees can be uprooted or can be cut off base).
Burst of materials such as volcanic rock fragments (bombs or volcanic rocks) thrown when volcanoes erupted and can be spread in all directions, so it can cause a forest fire, buildings fire and the death. The distance of burst material is very dependent on the amount of energy eruption, can reach hundreds of meters away. In addition to high temperatures (> 200 0C), the size of the material was large with a diameter of more than 10 cm.
Heavy ash rain occur when volcanic eruptions are in progress. The fine size material (ash and fine sand) is blown off by the wind and falls as the ash rain and its direction depends on the direction of the wind. Because of its fine size, this material will be very dangerous for breathing, eye, ground water contamination, plant destruction and contains acid chemical elements that can lead to corrosion of zinc and aircraft engines.
|Figure 11. Plants that die due to being covered by volcanic ash (Website: PVMBG)|
Lava flow is a magma that drip steam to the surface, its liquid (high viscosity) and high temperature (700-1200 0C). Because its liquid, the lava generally flows along the slope and burn whatever it passes. If lava is cold, then its form becomes rock (igneous rock) and the area through which it will become a stone field.
Lahar flow occurs on volcanoes that have crater lakes, occur simultaneously during eruptions. Water mixed material off volcano flows with a form of lahar flood. Lahar flow is very slow between 5-300 meters/day, its speed depends on the viscosity and slope of the slope. Humans can avoid saving themselves. Lahar can be divided into 2 types, namely lahar eruption and rainy lahar. Lahar eruption occurred due to explosive eruption on the volcano which has a crater lake, while rainy lahar formed due to rain that occurred after volcano erupted or after a long eruption. Lahar flow has a density of 2 – 2,5 kg/m3, can carry a variety of sizes, so that this lahar flow has a very large destructive and very dangerous, especially in the area of flow is quite tilted or sloping. Concrete buildings such as bridges can be destroyed in the blink of an eye.
Poisonous gas is a volcanic gas that can be instantly death when inhaled in the body. The gas is usually colorless and odorless. The emergence of Poisonous gases is not always preceded by volcanic eruptions because these gases can escape through cavities or fractures contained in volcanoes area. The main gas that usually appears is CO₂, H₂S, HCl, SO₂, and CO. What often causes death is CO₂.
Generally it can occur on submarine volcanoes, where the eruption of materials will provide great energy to push the seawater toward the coast to become a tsunami. The greater the volume of eruption material the greater the wave lifted to the ground surface.
Currently the volcano is always in control, so that volcanoes can be distinguished by volcanic activity based on direct observation is commonly called status of volcanoes, among others: awas, siaga, waspada, and normal.
Indicates a moderate or erupting volcano. The opening eruption starts with ash and smoke, potentially within 24 hours. Areas that are in danger of being emptied.
Indicates a volcano that is moving toward eruption or causing disaster. Increased intensive seismic activity, the data showed that the activity can be resumed to the eruption or lead to circumstances that can lead to disaster, eruption could occur within 2 weeks. Socialization in the region is threatened.
There is an increase in activity above the normal level. Increased seismic activity and other volcanic events. Slight changes in activity caused by magma, tectonic and hydrothermal activity.
There are no symptoms of magma pressure activity. Basic activity levels, routine observations, surveys and investigations
Land movement disaster or otherwise known as landslide is the process of moving rock/soil due to gravity and is a natural phenomenon controlled by geological conditions, rainfall and land use on the slopes. In recent years, the intensity of land disasters in Indonesia has increased, with the spread of the disaster area more and more widespread. This is caused by the increasing use of land that is not environmentally sound to vulnerable areas of land movement, as well as high rainfall intensity with long duration, or due to the increased frequency of earthquakes. a lot of settlements built around the hills are less concerned about the stability of slopes, rock structures and geological processes occurring in the region and did not realize the potential danger of a landslide at any moment life threatening.
Internal factors that cause the occurrence of landslide has weak cohesion of soil/rock so that the grains of soil/rock can be losse from its cement and move down by dragging other grains around it to form a larger mass. The weakness cohesion of soil/rock can be caused by porosity and permeability of the soil/rock and the intensive fracture of the soil/rock. While external factors that can accelerate and become a trigger soil landslide can consist of various complex factors such as slope slope, moisture changes of soil/rock because infiltration water, land cover and the pattern of land treatment, erosion by surface water, act humans like digging and another.
Ground movement gradually may cause the slope and cracking of the soil to cracking the foundations and facilities. The sudden landslide of the slope can break down the ground beneath the shelters and throw the buildings into the hillside (Figure 14). Landslides can destroy buildings, roads, pipes, and wires that are above his or crushing / buried below will be followed, as well as in living things.
Figure 14. Houses has burried by landslide (Noor, 2012)
Flood is a disaster that always repeats every year in Indonesia, it is noted that most occur in the rainy season. Based on the morphological, floods occur in countries with varying landscapes with their numerous rivers. Flooding in Indonesia generally occurs in western Indonesia, because the level of rainfall is very high compared to the eastern part of Indonesia. The growth of the population in Indonesia and the need for space as a place to accommodate human life and support its activities indirectly has played a role in the flood. Deforestation done to meet space needs has increased sedimentation in rivers, uncontrolled surface water and soil become water saturated.
Puddle and water flow with rapidly flowing pressure can tear down and sweep away people and animals in the depths of the water. Even floods can also knock down buildings damaged by water-induced foundations, ruins of buildings carried by water can also damage other buildings and may injure living things. Sewerage systems can be broken by floods resulting in pollution and sickness.
High climate variability leads to extreme wet and extreme dry events. In the event of extreme wet, the potential occurrence of floods and landslides increase, and vice versa, if there is extreme dry, then the potential for prolonged drought will be quite large, and can cause drought. Drought is the relationship between the availability of water that is far below the water requirement for life, agriculture, economic and environmental activities. Drought is one of the most serious problems in Indonesia. The cause is the decline of rainfall over a long period, which is the impact of the interaction of the atmosphere and the sea, as well as sea surface irregularities occurring in Indonesia and surrounding areas, the El Nino phenomenon, positive IOD (Indian Ocean Dipole), and the monsoon cycle. The incidence of El Nino and positive IOD resulted in reduced production of clouds and amount of rain over Indonesian territory as a result of decreasing sea surface temperature in Indonesia and surrounding areas.
Drought can be classified by characteristics and impacts. Specifically there are four types of drought, namely:
Drought will have an impact to human health, plants and animals. Drought causes the trees to die and the soil becomes barren which in the rainy season becomes easily eroded and flooded (Figure 16). The impacts of drought hazards resulted in the loss of food due to crops and dead livestock, farmers lost their livelihoods, many people starved and died, resulting in urbanization
|Figure 16 Drought causing dead plants in field (BNPB, 2012)|
Through the regulations of Head of BMKG (Kep. 009, 2010) difined about the extreme weather catastrophe as an event or series of events that threaten and disrupt the lives and livelihoods of people caused by extreme weather resulting in the occurrence of human casualties, environmental damage, property loss and psychological impact. The detailed explanation of extreme weather catastrophic events has been determined in the Regulation where the elements of the weather are considered extreme, ie the incidental and unusual weather events that can lead to losses, especially the safety of life and property, among others:
Noor, Djauhari. 2012. Pengantar Mitigasi Bencana Geologi, Program Studi Teknik Geologi: Fakultas Teknik Universitas Pakuan.
Robi Amri, dkk. 2012. Resiko Bencana Indonesia. Badan Nasional Penanggulangan Bencana (BNPB).
Unnamed. 2012. Tanggap Tangkas Tangguh Menghadapi Bencana. Buku Saku: Badan Nasional Penanggulangan Bencana (BNPB).