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Review Running Water Volcanoes Glaciers Earthquakes Rivers GEOL 131:Running Water GEOL 131:Running Water GEOL 131:Running Water How water gets into rivers? Where does it go? • Precipitation and snowmelt can: – Infiltrate • absorbed into ground • becomes part of groundwater – Run off (flow over surface) GEOL 131:Running Water Streamflow Characteristics • Flow velocity: speed of water movement • Channel steepness (gradient): Elevation change per unit distance • Channel roughness: Water can be slowed by a rough channel • Channel size and shape: Wide, shallow channel slower than narrower, deeper one with same cross-sectional area • Discharge: Volume of water moving through channel Discharge = width x depth x velocity GEOL 131:Running Water Erosion, Transport, Deposition • Erosion: – Quarrying: removal of blocks from riverbed – Abrasion: scraping of channel sides by particles in flowing water • Transport: – Suspended load, bedload, dissolved load – Capacity: max grain size river can carry • depends on velocity – Competence: max sediment load river can carry • Depends on discharge • Deposition – When velocity slows, sorted sediment deposits GEOL 131:Running Water Stream Channel Types • Bedrock – Cut into rock, steep-sided, V-shaped • Alluvial – Cut into sediment or soil – Two types: • Meandering: fine-medium grained sediment, consistent discharge • Braided: coarse sediment, highly variable discharge GEOL 131:Running Water Deltas and alluvial fans • Deltas: • At river mouths • Fine-grained sediment deposited when river enters standing water • Alluvial fans • Base of steep mountains GEOL 131:Running Water Floods • • • • Regional: usually seasonal Flash: Little warning, short duration Ice-jam: breakup of river ice Dam failures Volcanoes GEOL131: Volcanoes Eruptive Style • Why do volcanoes have different eruptive styles? – Dissolved gases (volatiles) – Viscosity: resistance to flow – Temperature • Hotter = less viscous (runnier) – Silica content • More silica = more viscous (thicker) • Explosive eruptions – fed by high-silica, low-temp magmas with high viscosity • Effusive eruptions – Fed by low-silica, high-temp magma with low viscosity GEOL131: Volcanoes Eruptive Materials • Lava – Aa and pahoehoe • Pyroclasts – Ash, lapili, cinders, blocks, bombs • Gases – Water vapor, carbon dioxide, others GEOL131: Volcanoes Three Types of Volcanoes Figure 4.14 GEOL131: Volcanoes Calderas • Pits caused by magma chamber collapse – Three types • Hawaiian-type: collapse of top of shield volcano caused by subterranean drainage from central magma chamber • Crater Lake-type: collapse of the summit of a large composite volcano flowing an explosive eruption • Yellowstone-type: collapse of large area, caused by discharge of huge volumes of silica-rich pumice and ash along ring fractures GEOL131: Volcanoes Other Volcanic Landforms • Basalt plateaus • Volcanic necks • Lava domes GEOL131: Volcanoes Plate Tectonics & Igneous Activity • Most volcanism occurs along tectonic plate boundaries – Divergent boundaries: decompression melting – Subduction zones: hydration melting • Ring of Fire: chain of active volcanoes around the Pacific Ocean • Intraplate – Not near plate boundaries Glaciers GEOL131: Glaciers What is a Glacier? • Mass of land-based ice – In motion downslope – Develop in high-latitude polar regions • Four types – Alpine (or valley) – Continental (or ice sheet) – Ice cap – Outlet GEOL131: Glaciers Formation and movement • Snow recrystallizes into firn – Ice crystals with texture of sand – Fuse to form glacial ice • Movement – Plastic flow • Most movement occurs this way • Flow in the solid state under high pressure – Basal sliding • Small amount of movement • Entire ice mass slides along base GEOL131: Glaciers Movement • Glacier budget – Balance between accumulation and loss of ice GEOL131: Glaciers Glacial Erosion • Depends on several factors: – Rate of glacial movement – Ice thickness – The shape, abundance, and hardness of the rock fragment contained in the ice at the base of the glacier – Erodibility of surface beneath glacier • Mechanisms – Plucking: loosens and lifts blocks of rock and incorporates them into the ice – Abrasion: ice and the rocks incorporated within slide over the bedrock, smoothing and polishing the surface below GEOL131: Glaciers Glaciated Mountain Valleys GEOL131: Glaciers • Drift Types of Glacial Sediment – General term for any sediment deposited by a glacier • Till – Deposited directly from melting ice – Unsorted • Stratified drift – Deposited by meltwater rivers – Well-sorted GEOL131: Glaciers Depositional features GEOL131: Glaciers Effects of ice age glaciers • • • • • Crustal subsidence and rebound Change in sea level Changes in rivers and valleys Proglacial lakes Pluvial lakes GEOL131: Glaciers Possible Causes of Ice Ages • Plate tectonic movement – Continents can move poleward • Variations in Earth’s orbit – Precession, obliquity, eccentricity • Others – Changes in atmospheric composition – Changes in Earth’s reflectivity – Cooling of ocean currents Earthquakes GEOL131: Earthquakes What is an Earthquake? • Earth vibration – Usually caused by movement on a fault – Strain energy is stored up along fault over time • Seismic energy propagates through planet’s interior in all directions GEOL131: Earthquakes Seismology • Study of earthquake waves • Seismograph: measures seismic wave magnitudes • Seismic waves – Body: travel through Earth’s interior • P (primary): push-pull motion; travel fastest; solids, liquids, and gases • S (secondary): movement at right angle to direction of motion; slower; solids only – Surface: travel in rock layers below surface GEOL131: Earthquakes Epicenter Triangulation S-P interval: delay between P- and Swave arrivals S-P = 5 min. S-P = 7 min. S-P = 11 min. GEOL131: Earthquakes Epicenter Triangulation Travel-time curve If S-P = 5 mins, distance to epicenter is 3500 km Repeat for other two stations GEOL131: Earthquakes Epicenter Triangulation Epicenter Plot distances from travel time curve on globe as circles Point where circles intersect is epicenter GEOL131: Earthquakes Size of Earthquakes • Intensity: degree of shaking at given locale based on damage and human perception • Magnitude: estimate of total energy released – 32-fold increase in energy for each increase of 1 on magnitude scale – Richter vs Moment • Richter: seismogram only • Moment: seismogram, total movement on fault, depth of movement, rock strength GEOL131: Earthquakes Earthquake Damage • Destruction from seismic vibrations – Direct damage • Shaking of structures • Amplification of seismic waves • Liquefaction – Indirect damage • Landslides: ground shaking causes loose sediments on slope to slump • Tsunami: failure in subduction zone displaces water, which spreads out radially in all directions GEOL131: Earthquakes Earthquake belts • Major earthquake zones include the Circum-Pacific belt, Mediterranean Sea region to the Himalayan complex, and the oceanic ridge system Exam 2 Reminders • Wednesday, June 7 at 9:35 am • 3 x 5 inch notecard – Handwritten – Both sides ok • Bring calculator – phones not allowed!
