Landscape yang terbentuk oleh Proses Denudasional

Landscape yang terbentuk oleh Proses Denudasional

DenudasiDenudasi adalah kelompok proses, apabila berjalan panjang, akan menurunkan seluruh permukaan bumi hingga mencapai rata dengan base-level.

Proses yang berkaitan dengan degradasi, yaitu:Pelapukan, yang menghasilkan regolith (debris dan soil)Pengangkutan, perpindahan material secara terlarut maupun takterlarut oleh erosi dan gerakan tanah.DenudasiDenudasi

DegradasiDalam hal ini proses utama adalah degradasi batuan (melalui pelapukan) , pengelupasan, erosi dan gerakan tanah.

Pengertian Pelapukan, Erosi, Gerakan Tanah dan PengendapanWeathering is the physical disintegration or chemical alteration of rocks at or near the Earths surface.Erosionis the physical removal and transportation of weathered material by water, wind, ice, or gravity. Mass wasting is the transfer or movement of rock or soil down slope primarily by gravity.Depositionis the process by which weathered and eroded materials are laid down or placed in a location that is different from their source.These processes are all very important to the rock cycle because over geologic time weathering, erosion, and mass wasting transform solid rock into sediments and soil that result in the redeposition of material forming new sedimentary rocks. Pelapukan (Weathering)Pelapukan adalah suatu proses perubahan fisik maupun kimiawi yang dialami oleh batuan, proses mana akan menghasilkan bahan rombakan (debris) dan tanah (Soil)Desintegrasi akan terjadi apabila aksi fisik (atau mekanik), kimia atau biologi (organik) atau ketiganya bersama-sama Di daerah beriklim sedang dan humid proses pelapukan kimia (dan biologi) bekerja dominan,Dibawah iklim dingin dan panas (kering) pelapukan fisik (mekanik) dominanPelapukan Kimiawi

9PELAPUKAN KIMIAWIThe most common alteration product of feldspars is kaolinite, Al2Si2O5(OH)4, which serves as a model for the formation of clays by weathering generally.The reactions of feldspars to kaolinite illustrate some of the basic trends:K, Na, Ca are highly soluble and readily leached by chemical weathering.Excess Si can be removed as silicic acid although quartz is relatively insoluble.Al is extremely insoluble, and is essentially conserved as source rock is converted to clays.Weathering is a hydration process, leaving H2O bound in the altered minerals.2 KAlSi3O8 + 9 H2O + 2 H+ -> Al2Si2O5(OH)4 + 2 K+ + 4 H4SiO4Note the H+ on the left-hand sideonly acidic water can drive this reaction

Natural waters are acidic due to equilibrium of carbonic acid with CO2 in the atmosphere CO2 (g) + H2O = H2CO32 KAlSi3O8 + 9 H2O + 2 H2CO3 -> Al2Si2O5(OH)4 + 2 K+ + 4 H4SiO4 + 2HCO3Alteration of rock transforms acidic rainwater into neutral surface or ground water, with bicarbonate the dominant species (relative to CO2 and CO32).Mg and Fe2+ are also readily leached, but Fe3+ is very insolublethe ultimate residue of alteration of mafic rocks is hematite.910Chemical WeatheringKnowing the chemistry of reaction of minerals to kaolinite, it is possible to reconstruct from the dissolved ions in stream water the amount of each source mineral that reacted with the water.

1011Pelapukan KimiawiSome minerals are congruently soluble in acidic water, leaving no residueThe most abundant is calcite: CaCO3 + H2CO3 = Ca2+ + 2HCO3 (the Tums reaction)Effects of dissolution (and precipitation) of calcite can be dramatic, to say the least.

SinkholeSpeleothemsKarst terrain11Mechanical Weathering (Pelapukan Mekanik)Mechanical Weathering - processes that break a rock or mineral into smaller pieces without altering its composition

Agents of Mechanical Weathering :thermal expansion and contractionmechanical exfoliationfrost wedgingabrasion by wind and waterplants and animalsPelapukan MekanikDefinisi- Fragmentasi fisik batuan dasar sebagaimana yang nampak pada atau dekat permukaan bumi (Defined - Physical fragmentation of bedrock as it is exposed at or near the earth's surface),Pelapukan fisik dapat disebabkan oleh pengurangan tekanan yang bekerja didalam batuan itu sendiri = menghasilkan retakan (Physical weathering accomplished by differential stress induced within rock = results in cracking),

Joints (retakan) batuan mengontrol pelapukan mekanikExfoliation

Dome Exfoliation

Unloading (Pelepasan Beban)

Frost Action

Frost wedging

Pertumbuhan Kristal dalam Celah Batuansaturated brine (containing sulfates, carbonates, chlorides, cracks/fissures in rockcrystals grow & expand & exert stress on surrounding rock of volume!crystals expand / contract with changes in temperature & often occurs in conjuction with chemical processescommon in arid to semi-arid environments e.g., tafoniOrganic processesin addition to chemical alterations (see above) plant root growth can open & exert stress within rock fracturesburrowing animals such as earthworms, termites and ants, moles, etc. churn sediments & increase air & water flow bioturbation.

Hydration & swelling

SOIL (Tanah)Soil adalah capuran material yang sudah lapuk , seringkali mengandung bahan organik , mineral fragments, air , dan udara.Soil terbentuk ribuan tahun yang lalu dan ketebalannya dapat mencapai 60 meters atau hanya beberapa sentimeter saja.Iklim, lereng, jenis batuan, jenis vegetasi, dan panjang waktu proses pelapukan, kesemuanya akan menentukan jenis soil yang terbentuk.Komposisi Soil (Tanah)In addition to the things we spoke of in soil already, most organic matter in soil comes from plants. The other organic matter comes from microorganisms. Decayed organic matter, such as plants, turns into a dark colored material called humus, which serves as a source of nutrients for plants. Humus gets mixed into the ground by worms, insects and rodents that burrow into the soil. Profile SoilSoil memiliki perbedaan lapisan-lapisan yang disebut horizon-horizon yaitu sebagai penyusun profil soil Ada 3 horozon soil (yaitu; Horizon A, B, dan C)Horizon A, disebut topsoil yaitu soil bagian paling atas, biasanya tertutup oleh litter dari unsur daun dan material organik lainnya yang dapat merubah jadi humus oleh dekomposisi organisma, humus akan menahan erosi dan evaporasi dari soil, Topsoil mengandung humus lebih banyak daripada partikel-partikel mineral dan batuan (daripada profil soil lainnya), Humus memberikan warna lebih gelap pada topsoil dan mengandung nutrisi untuk pertumbuhan tanaman

Profile SoilB Horizon lies underneath the A horizon and has less organic material. This makes it lighter in color than an A horizon, and there is less humus.A B horizon is less fertile, and contains material that has moved down from the A horizon by a process called leaching. Leaching is the removal of minerals that have been dissolved in water (coffeemaker). Profile SoilC horizon consists of partially weathered rock and it is the bottom most and thickest horizon in a soil profile.It has hardly any organic matter, its not affected by leeching, and is lightest in color of all horizons.You find a rock in a C horizon. This rock will eventually become horizon A and B through erosion and weathering.We call the rock in C horizon parent material.Karakteristik SoilKedalam :> 150 Cm : very deep (sangat dalam)100 150 cm : deep (dalam)50 100 Cm : moderately deep (kdlman menengah)25 50 Cm : shallow (dangkal)< 25 cm : very shallow (sangat dangkal)Kandungan humus :Tekstur : direkomendasi 2 klassifikasi :oleh USCS (Unified Soil Classification System),USDA Soil Survey Manual (1953)Surface StoninessRockiness28Erosion and TransportBetween weathering and sedimentation, matter must be transported from source to destination. This is erosion.Modes of transport:Gravity (short distances and steep slopes)Wind (small particles only)GlaciersWaterSurface runoff carries dissolved, suspended, and bed loadsGroundwater flow only carries dissolved loadAll these mechanisms carry products of physical weathering and insoluble residues of chemical weathering.Only water transport carries away leached soluble products of chemical weathering.Erosion (Erosi) adalah suatu group proses yang bekerja pada material tanah atau batuan yang menghilangkan dan melarutkan dan memindahkan setiap bagian dari permukaan bumi2829Erosion and TransportCertain modes of transport physically modify and physically and chemically sort particles en route.Size sorting by surface water runoff flow:

Current of a given velocity can generally carry all noncohesive particles smaller than a critical size; since current velocity drops with decreasing slopes from mountains to lowlands, it follows that sediments evolve from poorly sorted and coarse-grained near source to well-sorted and finer grained with increasing transport distance. 29ErosiJenis-Jenis ErosiTidak terdeteksiSheet dan rill erosion < 50 Cm depthRill dan Gully erosion 50 150 Cm depthGully dan ravine erosion > 150 Cm depthRiver erosion, verticalRiver erosion, lateralWind erosion (deflation)Other form of erosionRate of activityNoneSlightModerateSevereArea of affected :< 25%25 0 50 %50 75 %> 75 %Jenis-jenis Erosi

Rill erosionGully erosionSheet erosion32Erosion and TransportChemical sorting with increasing transport distance is like a continuation of chemical weathering during intermittent times when particles are temporarily deposited before further transport; most stable minerals are transported the furthest.Textures of particles are modified by abrasion during wind or water transport. Close to source particles are angular; far from source particles are rounded.

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MASS MOVEMENT (GERAKAN TANAH)Mass movements include: Landslides Rock falls Avalanches Mud flows Debris flows Creep

KLASSIFIKASI GERAKAN TANAH(Varnes, 1978)Type of MovementType of materialBedrockEngineering SoilPredominantly coarsePredominantly fineFallsRock FallDebris FallEarth FallTopplesRock ToppleDebris ToppleEarth ToppleslidesRotationalFew UnitRock SlumpDebris SlumpEarth SlumpTranslationalMany UnitRock Block SlideRock SlideDebris Blok Slide

Debris SlideEarth Block SlideEarth SlideLateral SpreadRock SlideDebris SpreadEarth SpreadFlowsRock FlowDebris FlowEarth FlowsComplex Combination of two ore more principles type of movementKlassifikasi Gerakan Tanah

Klassifikasi Gerakan Tanah

Carson and Kirby, 1972 in Ritter, et al., 2002Classification of Mass Movementsbased on water content and speed of movementLANDSLIDES

Anatomy of a rotational landslideDebris flows or mud flows

Debris flowMud flowROCK FALL

CREEP (RAYAPAN)