II. LITERATURE REVIEW
2.1 Natural Hazard Assessment
Natural hazard is “the probability of occurrence within a specific period of time in a given area, of a potential damaging phenomenon” Cepero, 2003. The
disasters that natural hazards can cause are largely the result of actions by man that increase vulnerability, or lack of action to anticipate and mitigate the potential
damage of these events. Typically, a number of types of hazards resulted from a volcanic activity.
Each hazard poses different risks affecting different areas. This is the key difference between eruptions and the other principal natural hazards, floods and
earthquakes. The most threatening hazards include pyroclastic falls, pyroclastic flows and surges, lava extrusions flows and domes, lahars, debris avalanches
and volcanic gases. This study deals with mud volcano hazard.
2.1.1 Mud Volcanoes in East Java, Indonesia
A mud volcano is a small volcano-shaped cone of mud and clay, usually less than 1-2 m tall. These small mud volcanoes are built by a mixture of hot
water and fine sediment mud and clay that either 1 pours gently from a vent in the ground like a fluid lava flow; or 2 is ejected into the air like a lava fountain
by escaping volcanic gas and boiling water. The fine mud and clay typically originates from solid rock-volcanic gases and heat escaping from magma deep
below turn groundwater into a hot acidic mixture that chemically changes the rock into mud and clay sized fragments USGS, 2008. Mud volcanoes are not
common and can occur both on the surface and at ocean bottoms worldwide. They are often associated with petroleum deposits.
The Sidoarjo mud flow or Lapindo mud, also informally abbreviated as
Lusi , a contraction of Lumpur Sidoarjo lumpur is the Indonesian word for mud,
is an ongoing eruption of gas and mud in the subdistrict of Porong, Sidoarjo in East Java, Indonesia 20 kilometers south of Surabaya. It is considered to be a
mud volcano. It appears that the flow will continue indefinitely and so far all efforts to stem the flow have failed Awad, 2006.
Figure 2.1 The continuous mudflow has submerged various villages
e mud was ranging from f the mudflow, to 0.1 to 0.6 metres at the
edges
writing, the flow is continuing. On 21 June 2006, Lapindo Brantas the owner of the well calculated the
volume of mud emitted since 29 May 2006, based on surface and depth measurements using Global Positioning System. On that date, the volume was
estimated to be 1.1 million m
3
of mud. The depth of th 3.5 to 6.4 metres around the source o
of the flood zones. Although the flow is not continuous and the mud volcano is intermittently active, the estimated average volume of emitted mud
over that period would have been over 40,000 m
3
day UN, 2006. At the time of
8
2.1.2 Volcano Hazard Assessment
When a normally quiet volcano begins to show signs of restless activity, people
ture eruptions USGS, 2000. Even when a volcano is not showing signs of restlessness, these answers are important for long-
planning purposes, including emergency-response planning and deciding where
sources and valuable environmental features that are within
ensure adequate data and information have been made available for use in the typically want to know what type and size of eruption might occur and
where potentially hazardous areas are located. Answers to these questions are critical to people and public officials who have to prepare for impending volcanic
activity. Volcano-hazard assessments help to provide the answers. Volcano-hazard assessments identify the location of potentially hazardous
areas and estimate the severity of fu
term to build new infrastructure, such as new buildings, power-generating
facilities, and transportation routes.
2.2 Vulnerability Assessment
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