As an introduction, dunes are product of aeolian environment. Aeolian environment involves intensive wind to transport and deposit sediments. Dunes are the accumulation of loose sand which has particular shape due to gradual influence of airflow. Typical sizes of dunes are 5 – 30 meters high and 50 – 500 meters across. An environment capable of forming dunes must sustain wind throughout the year. Several factors take place in the formation of Parangtritis dunes are located in the south of Yogyakarta, extending from estuary of Opak River to Sewu Mountains Karst. Parangtritis beach is a part of Yogyakarta basin. In this area, wind dominantly blows in SE – NW direction, with velocity of 1,19 meter a second.
Sediments in Parangtritis dunes came from three sources: Mount Merapi, WonosariPlateu, and Progo Hills. Based on lithology, Mount Merapi pulls out andesite, WonosariPlateu composed of carbonate rocks, and Progo Hills has all types of rock. The majority of sediments composing Parangtritis dunes are quartz, hematite – magnetite, and plagioclase. Minor constituents belong to lithic fragments, hornblende, and pyroxene. Grains in Parangtritis dune are generally sub-angular.
Almost all types of dunes have been built in Parangtritis. There are three dominant dunes in Parangtritis: Barchans, linier, and parabolic dunes.Barchans have horns which face in the same direction of the wind.When two directions of prominent wind at nearly 90o blows in desert, linier dune with symmetric ridge, straight or sinous, is formed.Moreover, parabolic dune builds horn which is perpendicular to the wind direction. Vegetation commonly affects the formation of this dune.
On average, barchans move 40 mm a year in the direction of the wind. In Parangtritis, Barchans has slip face angle of 32o to 40o and cross-lamination of 24o – 30o. Ripple index, which is the ratio of crest-to-crest distance to crest-to-trough distance, ranges from 4,5 to 6. Barchans tends to form better morphology toward east. Linier dune crosses in SE – NW and NE – SW direction with cross-lamination angle of 42o. In addition, linier dune has approximate height of 2,5 meters and length of 50 meters. Meanwhile, parabolic dune in Parangtritisis the least of the three. Vegetation, such as shrubs and coconut trees, controls the formation of this dune.
As a conclusion, the formation of dunes in Parangtritis is an evidence of intensive wind in this area long ago. A geological approach of this area reveals the wind movement in the past. Most important of all, Parangtritis dunes should be a prominent site for geoscience students to learn. In this outcrop, we are shown that even wind can sculpture vast area of sand, wind can make changes. And we, obviously, can spark sustainable living on Earth.
We live on Earth along with its beauty, precious resources, and disastrous hazards.
Aldo Febriansyah Putra
Gloria Gladis Sondakh
Ilham Bayu Nur Fachrozi
Tangguh Satria Pamungkas
American Association of Petroleum Geologists
Universitas Gadjah Mada – Student Chapter
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