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Pendahuluan Bentuklahan di muka bumi berkaitan dengan aktivitas dari kulit bumi (bentuk, susunan, lapisan
Dinamika dan Pembentukan Muka Bumi
bumi, dan perubahan dalam bumi) ada dinamika, dan Aktivitas dari luar bumi (pelapukan, pengangkutan dan pengendapan)
Prosesnya lama, melibatkan: Tenaga dari dalam bumi (endogen) Tenaga dari luar bumi (eksogen)
Proses-proses yang berkaitan dengan pembentukan lahan
1. Proses eksogen
Proses pembentukan mulai awal sampai terbentuknya relief muka bumi
2. Proses endogen 3. Pengaruh topografi dan manusia
TEORI PEMBENTUKAN ALAM SEMESTA (Lapplace)
Teori Pembentukan Relief Bumi Teori Kontraksi (Contraction Theory / Theory of a Shrinking Earth) Teori Laurasia-Gondwana Teori Pergeseran benua (Continental Drift Theory) Teori Konveksi (Convection Theory) Teori Pergeseran Dasar Laut Teori Lempeng Tektonik
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EARTH INTERIOR
Earth’s Interior Three Principal Layers Each has different Composition and density (mass/volume).
CORE: • • • •
Inner layer Density = high Composition is primarily iron and nickel. Contains two parts • Inner core is solid. • Outer core is liquid.
MANTLE:
The apple and the structure of the Earth. Ever wondered what our earth is made of? Think of it as an apple. An apple constitutes the skin, the pulp and the core in the middle. Similarly, the earth is made up of the thin outermost layer called the crust, the innermost part called the core, and the part in between them called the mantle.
• • • • • • • •
Middle thin layer Density = medium Composition is silicon and oxygen-based but also includes iron and magnesium. Consistency is plastic. Contains two parts, Upper and Lower Mantle.
CRUST: • Outermost layer • Density = low • Composition is silicon and oxygenbased minerals • and rocks. • Crust is extremely thin. • Consistency is rocky. • Composed of two general types. • Continental crust • Oceanic crust
Cutaway views showing the internal structure of the Earth
Inti Bumi
Beban besar, tekanan besar
The Crust (Oceanic and Continental).
Subdivisions of the Earth’s Interior Within these three principal layers are subdivisions. Crust consists of OCEANIC CRUST (brown) CONTINENTAL CRUST (green).
• The outermost sublayer is the most active geologically. • Large scale geological processes occur, including earthquakes, volcanoes, mountain building and the creation of ocean basins. • Contains parts of the upper mantle and all of the crust. • Called the LITHOSPHERE (rock layer). • Below the lithosphere resides the ASTHENOSPHERE (weak layer).
Oceanic crust is thin (8-10 km), dense, and found below ocean basins (blue). Continental crust is thicker (20-70 km), has low density and forms the bulk of continents. The crust rides on the very upper most portion of the mantle.
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• Lithosphere is a strong layer, but brittle. • Represents the outer approximately 100 km of the Earth. • Thicker where continents exist, thinner under oceans. • • • •
Asthenosphere is part of the upper mantle. Asthenosphere is heat softened and acts like a plastic. It is weak, slow flowing, yet solid rock. Generally 100 to 350 km beneath Earth’s surface.
The Theory of Plate Tectonics Steps in Development 1. Benjamin Franklin (late 1700s) Recognized that crust of Earth was a shell. Surface could be broken and parts moved about. 2. Alfred Wegener (1912) German meteorologist-geophysicist Proposed theory of Continental Drift. Proposed continents float on a denser underlying interior of the Earth. CONTINENTS periodically break up and DRIFT apart.
200 jt jt Tahun Tahun Lalu Lalu 135 225 jt Tahun Lalu 65 jt Tahun Lalu
JURASSIC TRIASSIC PERMIAN CREACEUS SAAT INI
Evidence in support of Continental Drift 1. Continental Fit Sir Francis Bacon (1620) noted that the continents might fit together. Made observation after seeing some newly made maps.
2. Habitats of Modern Organisms • Hippopotamus found in Africa and Madagascar. • Marsupials in Australia. • Indicate some migration and evolution took place before and after drift began.
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3. Fossil Record • • •
Wegener used the fossil record. Found fossils of plants and animals that were found on several continents. Included animals, Cynognathus, Lystrosaurus, Mesosaurus, and plants Glossopteris.
4. Similar Rock Types Across Ocean Basins • Mountains of Northern Hemisphere similar in Greenland, NA, and • Europe. • Also similar rocks between South America and Africa.
The plates drifted through the years to where they are now.
5. Ancient Climates • Glacial striations found in India, Australia, South America and Africa. • Radiate from a point in southern Africa. • Also coal deposits found in presently cold regions, such as Norway. Convection currents and plate movements.
Magma heats up and rises.
Akibat pergerakan lempeng tektonik Kemungkinan: Kecepatan sama tinggi Magma sinks, plates dragged towards each other.
Yang satu tinggi yang satu rendah Kecepatan sama-sama rendah
Batas Magma spreads out, plates move apart.
Batas menyebar, semakin menjauh biasanya
berupa rangkaian punggung dasar laut Batas terpusatkan, gerakan memusat/mendekat
gunungapi dan palung laut yang sejajar dengan batas Batas menggunting, gerak lereng sejajar dengan arah berlawanan sepanjang perbatasan
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Types of Plate Boundaries
convergent
divergent convergent
divergent
transform
hot spot
Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.
As magma meets the water, it cools and solidifies, adding to the edges of the sideways-
Sea floor Spreading.
Divergent Plate Boundaries Occur along spreading centers where plates are moving apart The Mid-Atlantic Ridge: Spreading at ~2.5 cm/yr
Computergenerated detailed topographic map of a segment of the Mid-Oceanic Ridge. "Warm" colors (yellow to red) indicate the ridge rising above the seafloor, and the "cool" colors (green to blue) represent lower elevations. This image (at latitude 9° north) is of a small part of the East Pacific Rise. (Imagery courtesy of Stacey Tighe, University of Rhode Island.)
Subduction is the process in which one plate is pushed downward beneath another plate into the underlying mantle when plates move towards each other. The plate that is denser will slide under the thicker, less dense plate. Faulting occurs in the process. It is the process in which rocks break and move or are displaced along the fractures. The subducted plate usually moves in jerks, resulting in earthquakes. The area where the subduction occurs is the subduction zone. A long, narrow, deep depression forms in this area. It is called an oceanic trench. The jerky movement, as well as the friction between the plates causes much heat, and together with the heat from the mantle and from radioactive decay, causes the subducted plate to melt. Magma is produced by the melting plate. It rises through fractures in the crust and reaches the surface to form volcanoes. In the end, the heat may be so intense that large areas of the crust are melted, forming granites just below the surface. The boundary of such plate movements is 'destructive' as part of the plate melts during subduction and is destroyed. As plates move towards each other, the opposing force between them is so great that the massive folding or the bending of rocks also occurs at the edges of the less dense plate. A range of fold mountains, such as the Himalayas, is formed.
Subduction forms oceanic trench
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Convergent Boundaries The Ring of Fire (lots of volcanoes) outlines subduction of Pacific plate
Convergent Boundaries Ocean-Continent Convergence Mount St. Helens
The Andes
Convergent Boundaries
Convergent Boundaries Continent-Continent Convergence
Ocean-Ocean Convergence
Mount Fuji
Mount Everest
The layer of the Earth we live on is broken into a dozen or so rigid slabs (called tectonic plates by geologists) that are moving relative to one another.
When plates move, everything on them moves with them. North American Plate moving west, Eurasian Plate moving east. Rate is about 5-10 cm/yr. Over long periods of time, movement is large.
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Pola Penyebaran Patahan di Bumi
Gaya Tektonik Tektonik Epirogenesa Gerakan vertikal yang lambat dan meliputi daerah yang luas Macam:
Epirogenesa Positif: ke dalam bumi, karena beban (sedimen, lava, dll) Epirogenesa Negatif: ke luar, berupa pengangkatan
Tektonik Orogenesa Gerakan tektonik meliputi wilayah yang sempit Pembentukan pegunungan
Struktur Diastropik Struktur pelapisan yang disebabkan oleh gerak
a.
Pelengkungan:
Gerak vertikal yang tidak merata di suatu daerah khusus yang berbatuan sedimen, semula horisontal menjadi vertikal
diastropik: Pelengkungan (warping) Pelipatan (fold) Retakan (joint) Pengangkatan (fault)
b.
Pelipatan:
Angkatan yang memiliki tenaga tidak sama menghasilkan pelipatan yang memanjang dan menghasilkan antiklin (dan sinklin jika terbentuk dua antiklin)
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c.
Retakan (jointing)
Retakan batuan pada bidang belah alaminya. Bisa terbentuk karena peregangan batuan yang disebabkan pemuaian batuan (pengaruh panas) Dapat membantu percepatan pelapukan batuan, karena air dapat masuk ke dalam batuan Jika hubungan antar batuan cukup lemah, gaya gravitasi pada lereng curam dapat melepaskan batuan dari tempatnya. Rectangular joint pattern in sandstone
d. Patahan (faulting) Berdasarkan arah gerakan: Transcurrents fault / Strike-Slip Fault, gerakan
horisontal, arah berlawanan
Dip-Slip Fault, arah miring ke bawah Oblique Fault, arah saling menjauh Rotation Fault, memutar pada bidang patahan
Berdasarkan bentuk patahan:
Selanjutnya pelajari materi kuliah minggu ke 3
GUNUNG BERAPI
Graben, turun Horst, naik Fault Scarp, dinding terjal yang dihasilkan oleh patahan,
dimana satu blok bergeser lebih tinggi
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