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The Rock Cycle

The Rock Cycle

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  • Anybody know what type of rocks these are?
  • solid Iron inner core, liquid outer core, semi-solid Mantle (magma)
  • Crystal structure can be cubic, hexagonal, orthorhombic, tetragonal, octahedral, etc.
  • The slow cooling formed rocks with large crystals. Granite is an example of a rock that cooled slowly and has large crystals.
  • Granite
  • Basalt is an example of this type of rock. Obsidian is an example of another extrusive igneous rock that cooled so fast that it has no crystals and looks like shiny, black glass. Pumic and Scoria - bubbles trapped in the lava form holes as the rock cools too quickly for the gasses to escape.
  • Incandescent lava fountains play above an eruptive fissure at Krafla volcano in NE Iceland on September 6, 1984. After a quiet interval of 33 months, an eruption began on September 4 along a fissure extending from Leirhnjúkur 8.5 km to the north. Initially, the fissure was active along its entire length, but later lava production was highest at the northern end of the fissure.
  • Shield volcanoes derive their name from their low-angle profile , which resembles the broad shields used by Hawaiian warriors. They are formed primarily by the successive accumulation of fluid lava flows, which descend from summit or flank fissure systems. Although shield volcanoes are not as visually dramatic as stratovolcanoes, they are often much larger features. Oceanic shield volcanoes such as those in the Hawaiian Islands can rise as much as 8000 m above the surrounding sea floor and 12,000 m above their actual bases, which have sagged due to the immense mass of the volcano. Their volumes can exceed that of stratovolcanoes by several orders of magnitude. Most shield volcanoes are formed of fluid basaltic lava flows. Calderas are large volcanic depressions formed by collapse of the summit or flanks of a volcano into underlying chambers evacuated by very large explosive eruptions or the effusion of large volumes of lava flows. Earth's calderas range from a kilometer to as much as about 100 kilometers in width; many contain scenic caldera lakes. Calderas may be simple structures formed during an eruption that truncates either the summit of a single stratovolcano or a complex of multiple overlapping volcanoes, such as at Crater Lake in Oregon. Other calderas are compound structures formed incrementally as a result of multiple eruption-related collapses, such as the massive 30 x 100 km wide Toba caldera in Sumatra, which was formed during four powerful explosive eruptions during the Pleistocene. Calderas are most often defined as depressions produced as a result of large-scale eruptions, but the word has also been used as a morphological term that encompasses volcanic depressions formed by erosion or large volcanic landslides. Stratovolcanoes (also known as composite volcanoes) are what most people associate with the word volcano. These towering peaks rise hundreds to several thousand meters above their surroundings, often visually dominating the landscape around them. As their name implies, they are formed of stratified layers of both viscous lava flows and fragmental material. Classic symmetrical stratovolcanoes such as Shishaldin in the Aleutian Islands and Mayon in the Philippines are the exception rather than the rule. Most stratovolcanoes are complex structures formed by multiple eruptions from summit and flank vents. Compound stratovolcanoes may form when the focus of eruptions shifts, forming multiple overlapping edifices. Some stratovolcanoes may form in a few thousand years, but may remain active for tens to hundreds of thousands of years. During their lifespans, dormant intervals may also last tens of thousands of years.
  • Which of these would be considered “Biological” weathering? Exfoliation is most common in granite (intrusive igneous); because of it's lattice structure (due to crystallization), sheets will fracture and "peel" parallel to the rock surface.
  • Any Biological weathering here? Lichen on rocks secrete a chemical that slowly eats away at the minerals. Rust = a chemical reaction where iron reacts with water and/or oxygen to form ferric iron oxide (hematite).
  • Erosion and Weathering affect grain shape: When a rock first breaks, it is very sharp. We call this angular grain shape. Over time, these rough edges get smoothed out. The smoother a rock is, the longer it has been exposed to weathering.
  • Wind erosion (like that of the dust bowl of the 1930s). Water erosion (roadway is washed away). Glacial erosion (rocks embedded in ice are carried slowly downhill with the weight of the glacier).
  • Sedimentation rates vary from place to place, and at different times. Rates can range from .2cm to 1 m per 1000 year span.
  • What do you notice? How much “sediment” do you think was laid down because of this blast? (25 feet thick, with many layers “sifted” by the water)
  • efinition: Lithification is how soft sediments, the end product of erosion, become rigid rock ("lithi-" means rock in scientific Greek). It begins when sediment is laid down for the last time and is gradually buried and compressed under new sediment. Fresh sediment is usually loose material that is full of open spaces, or pores, filled with air or water. Lithification acts to reduce that pore space and replace it with solid mineral material. The main processes involved in lithification are compaction and cementation. Compaction involves squeezing the sediment into a smaller volume by packing the sediment particles more closely, by removing water from the pore space (desiccation) or by pressure solution at the points where sediment grains contact each other. Cementation involves filling pore space with solid minerals (usually calcite or quartz) that are deposited from solution or that enable existing sediment grains to grow into the pores. The pore space does not need to be eliminated for lithification to be complete. All of the processes of lithification can continue to modify a rock after it has first become a rigid solid. Lithification occurs entirely within the early stage of diagenesis. Other words that overlap with lithification are induration, consolidation and petrifaction. Induration covers everything that makes rocks harder, but it extends to materials that are already lithified. Consolidation is a more general term that also applies to the solidification of magma and lava. Petrifaction today refers specifically to the replacement of organic matter with minerals to create fossils, but in the past it was more loosely used to mean lithification.
  • Sedimentary rock is the only type of rock to contain fossils! WHY?
  • Can you guess how each of these was formed? Shoreline ripples, evaporation, conglomerate of river rock, estuary deposit.
  • Granite to Gneiss When granite is exposed to extreme pressure within the earth, it changes to the metamorphic rock gneiss. Notice how the gneiss has alternating bands of dark and light colors. These bands are made by the minerals in granite becoming realigned by pressure. This online animation shows you what this looks like. Note the effect of confining pressure on how the mineral grains are aligned and compare the alignment of the internal mineral grains to the outward appearance of the rocks. Alternating bands of mineral grains in a metamorphic rock is called foliation. Foliation occurs perpendicular to the direction of stress, as you can see from the diagram below.
  • Anybody know what type of rocks these are?

Geology - Part 1 Geology - Part 1 Presentation Transcript

  • Geology - Part 1 The Rock Cycle
  • How do we Learn about Earth’s History?• Archeology – The study of human life on Earth – Artifacts: objects made by humans such as tools, weapons, containers, etc.• Paleontology – The study of lifes history as revealed in the preserved remains of once-living plants and animals – Fossils: Any evidence of organisms that once lived on Earth• Geology – The study of Earths origin, history and structure – Rocks: solid masses of mineral matter (including metals, stones & gems)
  • This Big Ball We Call Home View slide
  • Where Do Rocks Come From ? View slide
  • Crystallization – magma cools into solid rockWell start here
  • Crystallization• Magma (melted rock from Earths mantle) cools with a regularly repeating (lattice) structure to form IGNEOUS rocks. • Intrusive: under- ground • Extrusive: above ground
  • Intrusive (underground) Slow LargeCrystallization Crystals MAGMA
  • Batholith: Yosemite’s Half-Dome
  • Igneous Intrusions• Dike: “veins” that run perpendicular to (cut through) the strata• Sill: sheets that run in the same direction (between) the strata• Batholith: huge, bulbous mass intruding surrounding strata deep underground
  • Extrusive (Volcanic ) Fast Crystallization SmallCrystals MAGMA
  • Igneous Extrusions: Magma Meets Air Lava (molten rock)Volcanic eruptions Fissure vent
  • IgneousExtrusions:Magma Meets Water Deep Sea Vents
  • Volcanic LandformsVolcanicEruptions
  • Types of Igneous RockGranite Scoria BasaltPumice Obsidian
  • The Rock Cycle
  • Weathering The breakdown of rocks into smaller pieces (sediment).• Physical (mechanical) – Size change• Chemical – Composition change• Biological – Physical & chemical
  • Physical Weathering from Freezing and Thawing Frost Wedging FrostHeaving
  • Plant Roots ExfoliationBurrowing of Animals Friction and Repeated Impact
  • Chemical WeatheringWater/Carbonic Acid Oxidation (rust) Living Organisms Acid Rain
  • Weathering Effect of Erosion• Small particles are broken off as rocks are carried away by ice, water and wind.
  • What type ofweathering is this?
  • Erosion & Transport – sediment is carried away
  • ErosionThe process by which water, ice, wind or gravity moves fragments of rock and soil.
  • Rivers, Oceans & Runoff Glaciers Wind and Landslides and soil creep Storms
  • Deposition – sediment is laid down
  • Deposition of Sediment Along with erosion, rocks and rocky particles (such as shell and bone) are transported and/or deposited in layers (called strata) by:• Icebergs (former glaciers) melting• Settling of biogenic ooze• Earthquakes• Volcanic eruptions• Floods and Hurricanes• Evaporation
  • Mt. St. Helens before eruption Mt. St. Helens aftereruption
  • Burial & Compaction – sediment pressed down
  • Burial and Compaction• Layers of sediment are laid down on each other• Particles of sediment are squeezed together by the weight of water and layers above• Solid minerals form in the spaces between sediment particles, holding them together• This process is also known as lithification
  • Sedimentary Rocks exhibit the following:• Stratification: the deposition of sediment into horizontal layers or “strata”• Lamination: several thin layers (< 1cm)• Superposition: deeper layers are older• Cross-cutting Relationships: intrusions younger than the strata they cut through• Fossils: evidence of life trapped in rock layers
  • Sedimentary rocks are softer than all other rock types
  • Deformation – rocks folded & split
  • Deformation Intense forces deep underground can twist, fold, or tilt existing rock into different shapes.Causes:• Pressure from slow, deep folding as tectonic plates collide• Tension from tectonic plates pulling away from one another• Shear from rapid surface movement along fault lines during earthquakes
  • • Experiment using layered sheets of wax – shows how rock layers tend to bend and fold before they break
  • Examples of Deformed Rocks
  • Metamorphism – chemical change of rocks
  • MetamorphismA change in mineral composition of existing rocks due to extreme pressure and/or heat deep within the Earth’s crust. Metamorphism• Regional: large animationarea such asmountain range insubduction zonewhere rocks arepulled/pushed• Contact: due tophysical proximity ofheat, usually frommagma intrusion
  • Metamorphic Rocks - the hardest typeof rocks found on earth Marble Gneiss Quartzite Schist Slate
  • Uplift – rocks pushed up to surface
  • Uplift The movement of Earth’s tectonic plates can cause a lifting up of previously buried rock layers.• Slowly where tectonic convergence occurs
  • Uplift• Rapid uplift: • during earthquakes • due to ice melting or erosion which removes a great weight from the land
  • Melting – rocks heated into semi-solid magma
  • Review: Major Rock Groups• Igneous – Formed from magma (molten rock) – Intrusive (plutonic): slowly cool underground – Extrusive (volcanic): quickly cool at the surface• Sedimentary – Form in layers at Earth’s surface, usually under water – Contain fossils• Metamorphic – Rocks changed by pressure and temperature
  • What Type of Rocks Are These?
  • In Conclusion…• The rock cycle demonstrates the relationships among the three major rock groups• It involves processes on the Earth’s surface as well as the Earth’s interior• It is powered by – the interior heat of the Earth – earth’s gravitational forces – energy from the sun• It connects the “hydrologic cycle” with the “tectonic cycle”