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A total water available of 1915 mm a year, equivalent to a flow rate 7360m3s-1. with un-equal distribution

in time and space, in many cases, water shortages have caused serious problems to ecosystems and society.

Monsoon rains drop 80% of the annual total during the half-year rainy season, and severe droughts with

widespread impacts occurring periodically during the dry seasons.

(H. Pawitan, G.S. Haryani, 2011)

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(H. Pawitan, G.S. Haryani, 2011)

The increasing number of critical watersheds in Indonesia has been recognized since the 1980s, with

22 critical watersheds and 13 million ha of degraded land in 1984.

This has increased to 62 critical watersheds with a total area of 59.62 million ha by 2005, with an

on-going deforestation rate of 1.09 million ha year-1(during the period 2000-2006).17

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Summit lava dome and andesitic lava flow

Volcaniclastic deposits from Merapi volcano: pyroclastic and lahar deposits on

the SW flank, lahar deposits along the radial valleys from the NW to the SE

Main cities

Pyroclastic deposits are abundant. For the last

two centuries, the activity of Merapi has

alternated regularly between long periods of lava

dome extrusion, and sudden dome-collapse.

At Merapi, lahars are commonly triggered by

high-intensity rainfalls (commonly 40 mm in 2 h)

from the tropical monsoon climate.

Drainageis very dense. Lahar-related hazards are

high in the downstream part of the 13 rivers,

below 600 m asl, which drain the volcano, from

Senowo River on the west flank to Woro River on

the south flank.

F. Lavigne, J.-C., 2002

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(NOVA)

A molten river , Mount Etna

Lava flow

Sector collapse

Pyroclastic flow

Ash fall

Mud flow

(Lahar)

Volcano disaster

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Volcano disaster

(Google earth)

Mount St. Helens

Lava flow

Sector collapse

Pyroclastic flow

Ash fall

Mud flow

(Lahar)

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Soufriere Hills Volcano

Lava flow

Sector collapse

Pyroclastic flow

Ash fall

Mud flow

(Lahar)

(Photovolcanicacom)

Volcano disaster

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Lava flow

Sector collapse

Pyroclastic flow

Ash fall

Mud flow

(Lahar)

Sakura island

Volcano disaster

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(Photovolcanica.com)

Mt Pinatubo volcano

Lava flow

Sector collapse

Pyroclastic flow

Ash fall

Mud flow

(Lahar)

Volcano disaster

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(Photovolcanica.com)

Mt Pinatubo volcano

Lava flow

Sector collapse

Pyroclastic flow

Ash fall

Mud flow

(Lahar)

Topic in Mt.merapi

Volcano disaster

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(BADAN GEOLOGI)

Pyroclastic flow

occurred once every

several years.

Direction are various.

Changing topology arefrequent.

In 2010,The big eruption

occurred and made a lot of

sediment.

There are many unstable

sediment in a slop,bring on Lahar .

Pyroclastic flow

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The riverbed are compose ofash and sediment which

Pyroclastic flow and Rahar bring.

A grain size are very small,

roughly 1mm,infiltration is low in this area.

When heavy rainfall comes,

Surface flow appears and

erode land, make gully.

Bed material in Code.R

(JSCE)

Changeable topology

Unique hydrology

Pyroclastic flow

Lahar

Volcano ash

Sediment in Mt. Merapi

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Sh ll GW i h f f M M i

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Shallow GW in south west foot of Mt. Merapi

Type-: Blongkeng R., Batang R.,Krasak R. WS

Formed in old age

Steady discharge though year

Water rises with heavy rain but slow

River water of Type-comefrom GW in the upstream of

Type-WS area.

There was Type-WS area

before the new pyroclasticdeposit formed.

Putih R.

Type-: Putih R., Bebeng R. WS

New pyroclastic deposit

Few surface flow without rainfall

Flow is formed rapidly with rainfall

(Numamoto, 1993)

Border of GW flow system is not same as the current

topographic boundary but similar to that of the past. 28

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Conclusion The availability of water resources in Java Island

has experienced a significant reduction.

The number of watersheds in Java Island are

increasing since 1980s.

Pyroclastic flow, Ash fall, Lahar flow are observed

in Mt. Merapi.

The pyroclastic flow , lahar and volcano ash bythe volcanic activity of Mt.Merapi makes

changeable topology and unique hydrology.

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SELAMAT KULIAH LAPANGAN

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