CHAPTER 2 NOTES -FOUNDATIONS OF GEOLOGY-

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1 CHAPTER 2 NOTES -FOUNDATIONS OF GEOLOGY- LESSON 2.1A: LAYERS OF THE EARTH GEOLOGY Geology- LAYERS OF THE EARTH Earth has 3 major layers based on their composition: o - the outer layer, made of solid rock. The crust is much (~6x) beneath the continents than beneath the ocean. It is even thicker beneath mountain ranges. Most of the crust is covered by a thin layer of and a thick layer of. The crust is made up of Oxygen, Silicon, Aluminum, Iron and several other materials. The composition differs based on whether it lies under continents or the ocean. o - Earth s middle layer. Made of solid rock. Has not been studied directly. Information comes from the study of earthquake vibrations or, and how they travel through the earth. The lower boundary of the crust, between the crust and the mantle is called the. The mantle has two parts, divided by a. - from Moho down to 400 km (250 mi)

2 - from transition zone to about 1800 mi below earth s surface. (aka: Gutenberg discontinuity)- separates the core and mantle. o - spans from the bottom of the mantle to the center of the Earthabout 4,000 miles beneath our feet. - is thought to be made of up of molten iron or nickel and in liquid form, due to intense heat. - thought to be solid iron or nickel, kept solid by the internal pressure. LESSON 2.1B: DRIFTING PLATES PLATE TECTONICS - the theory that plates and their movements affects geologic structures and processes. o - area where one plate slides beneath another. The sinking of one plate forms a trench, and the other plate is pushed up to form a mountain ridge or island. FAULTS - the fracture zone that forms when a layer of rock breaks and moves. o Large faults are often the site of. Three Types of Faults: o - occurs when rocks along one side of a fault sink vertically. Often form cliffs. o - occurs when rocks along one side of a fault move horizontally along the fault.

3 o - occurs when rocks on one side of a fault are shoved on top of rocks on the other side. FOLDS - form by the bending of rocks under a great force. o - rocks that fold downward. o - rocks that fold upward. LESSON 2.1C: MOUNTAINS MOUNTAINS Mountains are classified based on how they were formed. o - formed when molten rock erupts from a hole in earth s crust. Can be on land or water. May form very quickly. o - form when molten rock is forced beneath an overlying rock layer, creating a dome. Many of these are also a result of volcanic activity. o - formed when the edges of two adjacent tectonic plates were pushed together. These often form large mountain ranges, such as the Appalachians, Rockies, Andies and Himalayas.

4 o - these mountains form along a fault. Rocks on one side of the fault are forced upward, while rocks on the other side sink, forming a steep cliff on one side. TOPOGRAPHIC MAPS - shows an area s elevation and natural features, as well as man made structures. o Use to show the terrain s shape and elevation. - height above sea level. o Usually cover a. o Use colors, symbols and lines to represent. o Contour lines close together = slope. Spaced lines = slope. LESSON 2.2A: EARTHQUAKES AND FAULTS WHAT IS AN EARTHQUAKE? - when huge masses of rock strain against each other and suddenly snap free, releasing a huge amount of energy. - a weak earthquake.

5 Most earthquakes last less than, but smaller earthquakes or tremors, called follow an earthquake at frequent intervals for days or even months, gradually. - giant sea waves that often result from earthquakes that occur near or beneath a large body of water. - the study of earthquakes. - the sudden movement of rock masses along a fault. The primary cause of earthquakes. o This movement may be or. - rocks on either side of a fault spring back to a position of little or no strain at the moment of an earthquake, triggering vibrations in the earth s crust. - rocks along one side of a fault that are lifted higher, producing a small cliff. o - fault scarps with smooth-faced sides. - a strike-slip fault located in western California. LESSON 2.2B- EARTHQUAKE ZONES AND WAVES - the point at which an earthquake begins. - the point on the earth directly above the hypocenter. o The effects of an earthquake are usually at the epicenter.

6 TYPES OF EARTHQUAKES Earthquakes can be classified at the depths they originate. o - about 85% of all earthquakes o - 12% of earthquakes o - 3% of earthquakes. These earthquakes only occur in subduction zones where oceanic plates are though to be sliding under continental plates. EARTHQUAKE ZONES Most earthquakes occur in definite narrow belts or zones. o - also called the - the most active zone. About of all earthquakes occur here. o - earthquake zone. of earthquakes occur here. o - long chains of undersea mountains. Accounts for of earthquakes. TYPES OF WAVES (or waves)- a rhythmic push/pull motion in the direction of wave travel. o Travel and are the first felt at the earth s surface. Can travel through any. o Produce an motion at the earth s surface. o Usually cause damage.

7 (or waves)- produce a side to side rolling motion. o Waves occur at right angles to the direction of the wave. Can only travel through. o Produce a motion at the surface. o Can cause damage. - produced when P and S waves reach earth s surface. o The waves. o May be felt over greater because they do not weaken as they travel. o Cause the damage. - instruments used to record the vibrations caused by an earthquake. o Produces a record called a LESSON 2.2C- EARTHQUAKE LOCATION AND STRENGTH The an earthquake is from a seismograph station, the the interval will be between the arrival of the first P waves and the first S waves.

8 - helps alert people living in earthquake prone areas. EARTHQUAKE STRENGTH - a system for evaluating the effect of an earthquake. o Useful for recording the. - a mathematical model used to rate earthquakes based on their patterns on a seismograph. o Scale ranges from with each level being stronger, but more powerful in terms of energy released. - the most reliable method for measuring an earthquake s magnitude. ENGINEERING FOR DISASTER - buildings constructed on bedrock. Allows beams and joints to absorb shock, but the structure can be deformed during an earthquake. - building rests on isolatorss that absorb seismic energy. SEISMIC HAZARD MAPS

9 LESSON 2.3A: VOLCANOES VOLCANOES Volcanoes all share common characteristics. o - a central channel through which gases, ash and rock are ejected. o - molten rock which lies several kilometers beneath earth s surface. o - reservoir of magma. The source of the eruption. o - formed when materials ejected from the volcano accumulate to form a conical mountain. A bowl shaped often caps the cone. TYPES OF VOLCANOES Volcanoes are classified according to the materials their cones are made of. o - consist primarily of erupted volcanic ash and rock fragments called. This cone is composed of loose materials and does not grow as large as other volcanoes. Erosion occurs rapidly. Most are formed by a single, which may last several years. o - pours out large amounts of highly fluid lava in mild eruptions. Produces a broad, cone. The slopes of a shield volcano are usually built up over time and flow after flow of lava. Eruptions occur at central vents and from along the volcano s sides (called ).

10 o - produce both cinder and lava. Also known as. Produce symmetrical, wide-based mountains that consist of alternate layers of lava and cinders. Cone is formed from eruptions from the crater and mild lava flows out of cracks in the volcanoes flanks. Produces a cone than a shield volcano. VOLCANIC ACTIVITY Scientists classify volcanoes as active, dormant, or extinct, according to their level of activity. o - when a volcano has erupted within recorded history or is currently producing seismic activity. o - an inactive volcano that is believed to have the potential to erupt again. o - a volcano that will probably not erupt again. Almost all of the earth s volcanoes are concentrated into three main belts that coincide with the earths earthquake belts. o More than half of the world s active volcanoes are in the. o Another belt corresponds with the earthquake belt, o The third belt is associated with the. LESSON 2.3B: VOLCANIC ERUPTIONS VOLCANIC ERUPTIONS Volcanoes erupt without warning. o The first sign of an impending eruption is when part of a volcano.

11 o Minor may also precede the eruption by a few days or hours. The first explosions are usually of volcanic,, and. Eruptions may occur at intervals, or a continuous eruption may follow. Volcanic eruptions may continue for weeks, months, or years until the volcano is quiet once again. Like earthquakes, violet eruptions by undersea or island volcanoes can generate huge. Not all volcanoes erupt. The violence of a volcano s eruption depends on two factors: o The ( syrupiness ) of the magma. Less viscous magma is thin and flows easily out of the cone. Thicker magma does not flow easily and results in more violet eruptions. o The amount of contained in the magma. EJECTA - any substance emitted by a volcano. o - can be poisonous. o - molten rock. Glows bright yellow initially, then turns redorange, to dull red, then to a black/gray as it solidifies, forming volcanic rock. o - lava that hardens to form a smooth or ropy surface. o - lava that hardens into rough, jagged rocks with a crumbly texture. o - lava that is emitted underwater or flows into water before solidifying. o - particles or blocks of solid volcanic ejecta. o - fine pyroclasts that are light enough to be carried by wind. (less than 2 mm) o - larger volcanic ash particles (less than 64 mm) o - form when lava is hardened within the volcano and is ejected in a solid state. Solid and irregularly shaped.

12 o - form when lava is through high into the air in a liquid or semiliquid state and hardens into rock before it hits the ground. Almond or tear shaped. o - a superheated cloud of gas and volcanic ash that travels down the volcanic slope as an avalanche. VOLCANIC EXPLOSIVITY - scale from 0 to 8 used to measure the explosiveness of a volcano s eruptions. o Each number is more explosive than the previous. VOLCANIC STRUCTURE - huge bowl-shaped craters. Formed when magma chamber is emptied and collapses. - form when the surface of a large lava flow hardens, but the lava beneath continues to flow. IGNEOUS INTRUSIONS - masses of volcanic rock beneath earth s surface. o - when magma hardens in a vertical crack or fissure. o - when magma squeezes between two horizontal layers of rock, forming a sheet-like mass. o - a dome like intrusion formed by thick, stiff magma that does not flow easily. The uplifted rocks above laccoliths form round hills or domed mountains. o larger versions of laccoliths.