GEOMORPHOLOGICAL DEVELOPMENT OF THE MURIA PALAEOSTRAIT IN RELATION TO THE MORPHODYNAMICS OF THE WULAN DELTA, CENTRAL JAVA

Abstract

The research area is situated in the Demak, Jepara, Pati and Kudus
regencies of the CentralJava Province. The objectives of the research are: (1) the
investigation of the geomorphologic development of the Muria Palaeo-Strait in
Central Java and (2) the analysis of the morphodynamicsof the WulanDelta. A
morphographic- morphogeneticapproach was used to interpret the genesJsand
subsequent evolution of the coastal lowlands in the surroundings of the Muria
Volcano. The data analysis techniques, based on cause-effect assessment and
analogy, were implemented in four steps, such as: (a) descriptive, (b) comparative,
.(c) associative and (d) causative stages. The results of the research can be
summarized as follows: The coastal plain situated to the south of the Muria
Volcano was originally a shallow strait and subsequently became a mangrovecovered
tidal flat with many creeks. Ultimately this tidal flat evolved into an
alluvial/coastal plain with natural levees and back swamps. The coastal area in the
west was still inundated by the sea around 6,000 yrs BP. This is evidenced by the
14C-dating 6,530 + 120 yrs BP of a coral reef situated at 25 cms a.s.l. The present
beach ridge has an age 4,600 + 100 yrs BP and originated as a barrier bar. The
coastal area in the east is characterized by the occurrence of four sequential beach
ridge complexes at elevations of 580, 520, 220 and 125 cms respectively. They
have been 14C-dated 5,860 + 110 yrs BP, 5,090 + 100 yrs BP, 3,530 + 100 yrs BP
and 1,760 + 120 yrs BP. Since 1,760 yrs BP nofurther beach ridges wereformed,
a tidal flat developed instead. The shape of the Wulan Delta changed from actuate
to digit ate in the period of 1925 - 1995, mainly due to human interference with the
river for purposes of irrigation. The growth of the Wulan Delta affected the hydro
dynamical situation offshore of Jepara. These hydrodynamic changes resulted in
marine erosion in the rural areas in the Jepara Regency and chewier formation in
the rural areas of the Demak Regency.