East Java Province Hazards

Types of Hazard

According to historical data, East Java province has possibilities natural disaster occurrences such as landslide hazard, volcanic eruption, earthquake and flood explained as follows:

Mass Movement
Mass movement is movement in which bedrock, rock debris, or soil moves downslope in bulk, or as a mass, because of the pull of gravity. Mass movement includes from so slow movement to very rapid movement (McGeary et all). Mass movement can be categorized based on the movement mechanism as follows:

1. Flow implies the descending mass that moving downward is viscous fluid.

2. Slide means that the descending mass remains intact and moving along one or more well – defined structure. Two types of slide are transitional slide in which the descending mass moves along a plane approximately parallel to the slope of the surface while in rotational slide (slump), the descending mass move along a curved surface, the upper part moving downward and the lower part moves outward.

3. Fall occurs when material free – falls or bounces down a cliff.

Landslide is one type of mass movements in which the descending mass remains intact and moving along one or more well – defined structure. Landslide occurrence can be caused by two primary categories: internal and external factors or combination of both. Some internal factors triggering landslide occurrences are: lithology/material/soil, geological structure, relief and slope, stratigraphy and drainage pattern/density. Some external factor triggering landslide occurrences are climate controls, landform unit, hydrological condition, land use/land cover and human activity.

Volcanic Eruption
Volcanic eruption is a natural event resulting from the activities of the Earth’s inner core that may release some of the Earth’s energy accompanied by volcanic material i.e. ash, magma and pyroclastic lava. There are three types of major volcanoes that are marked distinctively based on size, shape and composition as:

1. Basalt dome or Shield volcanoes are broad, gently sloping volcanoes constructed of solidified lava flow. During eruptions, lava spreads widely and thinly due to its low viscosity. Because the lava flows from a central vent without building up much near the vent, the slopes are usually between 2° and 10 i.e. Kilauea, one of the volcanoes that form Hawaii Island.

2. Cinder cone or pyroclastic cone is a small volcano between 100 and 400 meters tall, made up of pyroclastic fragment ejected from a central vent. In contrast to the gentle slope of shield volcano, cinder cones commonly have slopes of about 30° i.e. Cerro Negro.

3. Composite volcano or stratovolcano is volcano constructed of alternating layers of pyroclastic fragments or solidified lava flows. Composite volcanoes are built over long spans of time. Eruption is intermittent, with hundreds or thousands of year’s inactivity separating a few years of intense activity. This type of volcano is the larger and better known volcanoes of the world i.e. Mount Fuji and Anak Krakatau.

From three types of volcanoes, the most hazardous and devastating volcano is stratovolcano because it has high explosive eruption involving pyroclastic lava flows which usually flows faster due to steep slopes and often combine with hazardous gas explosion. East Java province has 12 volcanic mountains, most of them categorize as composite or stratovolcano meaning that this area is highly prone to volcanic eruption disasters

Earthquake
Earthquake is a trembling or shaking of the ground caused by the sudden release of energy stored in the rocks beneath earth surface. Earthquake usually occurs in the area where plate boundaries meet and interact. Southern zone of East Java province is one area prone to earthquake and tsunami hazard since it is directly facing the subduction zone in the Indian Ocean and un-solidified soil properties.
According to Harian Sore, some historical data of earthquake shows that Banyuwangi and other areas around it was stricken by an earthquake struck with 4.9 Richter scale in September 10^th, 2004, ten years after tsunami disaster struck that area in 1994.

Drought
There are three types of drought known which are explained as follows:

• Meteorological drought, involves reduction in rainfall a specific period (day, month, season, year) below a specific month-usually.

• Hydrological drought, involves reduction in water resources (stream flows, lake levels, groundwater, underground, and aquifers) below a specific level for a given period of time.

• Agricultural drought is the impact of meteorological and hydrological drought on this particular area of human activity. Crops have particular temperature moisture and nutrient requirement during their growth cycle in order to achieve optimum growth.

Northern zone of East Java consist of topographic Karsts which mainly dominated by groundwater table, thus, in the dry season, this area may facing all of drought’s types above.

Tropical Storm
A tropical storm is a storm system characterized by a low pressure center and numerous thunderstorms that produce strong winds and flooding rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air (www.en.wikipedia.org). Some areas in East Java province suffer from this type of hazard causing some damages and losses.

Flood
A flood is an overflow of an expanse of water that submerges land, a deluge which may result from overflowing of water volume within a body of water, such as a river or lake escaping its normal boundaries. Some types of flood hazard based on the sources and the material carried out are:

1. Riverine floods are floods that triggered by monsoonal rain and high tide, categorized in:

• Slow kinds: Runoff from sustained rainfall or rapid snow melts exceeding the capacity of a river's channel. Causes include heavy rains from monsoons, hurricanes and tropical depressions, foreign winds and warm rain affecting snow pack.
• Fast kinds: flash flood as a result of e.g. an intense thunderstorm.

2. Estuarine floods (tidal floods) are floods that caused by a combination of sea tidal surges caused by storm-force winds. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category.

3. Coastal floods are flood caused by severe sea storms, or as a result of another hazard (e.g. tsunami or hurricane). A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category.

4. Catastrophic floods are flood caused by a significant and unexpected event e.g. dam breakage, or as a result of another hazard (e.g. earthquake or volcanic eruption).