Geography I: Key Geographical Skills and Physical Geography

This is Unit Ten of Social Sciences and History, part two of two: physical geography from faults to the climate record. Part one closed on reading a plate boundary from the stress its landforms record, pattern as process. This part reads the rest of the physical earth the same way: a fault from the motion of its blocks, a soil from its climate, a coastline from its sea, a climate from its temperature and rain. It ends on the climate record, where the anchor states a consensus and the course keeps every figure and every claim attributed to the anchor and its sources, because that is how a record is read. By the end you will be able to name a fault and place the focus. To say what weathering, erosion and water do. To say what drives currents and sea level. To read an air-mass code and tell weather from climate. And to classify a climate by Köppen and state what the record shows.

Three entries on faults, magma and tsunamis: naming a fault from its motion, the focus and the epicenter, how magma behaves, and four causes of one wave.

Naming the fault from the motion.

SSH 0923 Faults, Focus, Epicenter: Naming the Fault From the Motion

The exam describes rock motion and asks the fault type, or describes an earthquake and asks where it began, and Dastrup's terms answer both. Stress is force per area; strain is the response: elastic, reversible; ductile, permanent bending; brittle, breaking. Faults are where brittle deformation lets two blocks move. Normal and reverse faults show vertical, dip-slip motion between a hanging wall above the fault plane and a footwall below, the miner's lantern and the miner's feet: in a normal fault the hanging wall drops; in a reverse fault it rises. A strike-slip fault moves horizontally. The focus, or hypocenter, is the point of first rupture, always at depth; the epicenter is the surface point directly above it, the location news reports give, and seismic waves spread from the focus as body and surface waves. The block above the fault slid down: normal. The block above was pushed up over the block below: reverse. The fence line is offset sideways across the fault: strike-slip. The rupture began eight kilometers down: that depth is the focus, and the map point above it the epicenter. The trap is the epicenter as the origin; the origin is the focus, below. The second trap is hanging wall: it is the block above the plane whatever the motion.

Magma.

SSH 0924 Magma, the Geothermal Gradient, and Eruption Signs

Magma holds melt, solids and volatiles, dissolved gases, whose proportions govern its behavior. The geothermal gradient, the rate temperature rises with depth, averages about twenty-five degrees Celsius per kilometer in the upper crust. Eruptions are forecast from history, earthquakes, slope deformation, and gas, and volcanoes are active, dormant or extinct. Time and magnitude stay hard to pin down, Dastrup says.

Tsunami.

SSH 0925 Tsunami: Four Causes, One Wave

A tsunami, Japanese for harbor wave, forms in four ways: underwater earthquakes, volcanic eruptions, landslides, or extraterrestrial impacts. It travels outward in a circle at about five hundred miles per hour, with long wavelengths and low frequencies and deep-ocean crests only two to three feet high, so ships never feel it; height builds near shore. December twenty-sixth, two thousand four, Indonesia, is the anchor's case.

Five entries on weathering, erosion, ice and water: rock meeting the surface, the agents that move it, glaciers, where the water is, and streams and groundwater.

Weathering.

SSH 0926 Mechanical and Chemical Weathering; Soil

Weathering is rock meeting the surface: mechanical breakdown into fragments, and chemical change of minerals into forms stable at the surface. Its products are sediment and soil, a mixture of about forty-five percent minerals, five percent organic matter, and fifty percent pore space, with sand, silt and clay as soil texture. Warm climates mean chemical weathering and clay-rich soils. The soil records its climate.

Erosion.

SSH 0927 Erosion's Agents: Water, Wind, Ice, Gravity

Erosion removes weathered sediment, driven by water, gravity, wind, or ice, and liquid water is the principal agent. Streams carry dissolved, suspended and bed loads. Wind, strongest in arid regions, saltates sand and leaves desert pavement. Mass wasting is slope failure under gravity, shear force down the slope against normal force into it. Subsidence is slow in Venice and New Orleans, fast in sinkholes.

Glaciers.

SSH 0928 Glaciers, Continental and Alpine

Glaciers cover about ten percent of the land surface, near the poles and in high mountains; during ice ages they covered as much as thirty percent, and the Snowball hypothesis has nearly all Earth once iced. Continental glaciers are ice sheets flowing outward over flat ground; alpine glaciers flow down mountain valleys. Geologists read where ice was from what it left.

Where the water is.

SSH 0929 Where the Water Is; The Hydrologic Cycle

Oceans hold ninety-seven percent of Earth's water; three percent is fresh, most of it ice in Greenland and Antarctica. A reservoir is any storage location, ocean, glacier, pond or atmosphere, and residence time is how long a molecule stays. The hydrologic cycle moves water among them, streams returning land's rain to the sea. Water expands when frozen.

Streams and groundwater.

SSH 0930 Streams, Floods, Groundwater

Streams are the most important agents of erosion and sediment transport. Floods come when precipitation exceeds what ground and channels can carry, and flash floods follow brief heavy rain. Groundwater fills pore space; porosity is that share, primary between grains, secondary in fractures, and most wells draw from within a hundred meters. Marsh, swamp and bog are three wetlands.

Two entries on oceans and sea level: what drives the currents, and what has moved the sea.

Currents.

SSH 0931 Surface Currents and the Coriolis Effect

Oceans, seventy percent of the surface, move heat from equator to poles by wind-driven surface currents and density-driven deep currents. Surface currents arise from three things: global wind patterns, the Earth's rotation, the Coriolis effect, and the shape of ocean basins, Northern Hemisphere currents circling clockwise. Global winds follow unequal heating. The anchor's wind chapter is unwritten.

Sea level.

SSH 0932 Sea Level, Eustatic and Accelerating

Eustatic sea-level change is global, from land ice or the seafloor's shape. Over twenty thousand years the sea rose about one hundred twenty-five meters from glacial melting, then slowed to about zero point seven millimeters a year, accelerating from about eighteen seventy, while seawalls, groins and dams starve beaches. Anthropogenic warming is the anchor's cause for the acceleration.

Five entries on weather and climate: radiation in and out, the controls of temperature, air masses by code, three storms, and weather against climate.

Radiation.

SSH 0933 Shortwave In, Longwave Out

The sun drives weather and climate, generating energy by thermonuclear fusion of hydrogen into helium. Its electromagnetic energy spans shortwave to longwave; the Earth receives shortwave radiation and emits longwave, and the balance between them sets temperature. Precipitation needs moisture, instability and condensation nuclei. The anchor's two chapters give the sun's mass share differently, and neither is voiced.

The controls of weather.

SSH 0934 Latitude, Water, and the Other Controls of Weather

Latitude is the first and most significant control of temperature: the equator absorbs more than it radiates, the poles the reverse. Water needs five times the energy per degree, specific heat, so coasts change slowly and continental climates sit far from water. Ocean currents, altitude and mountain barriers follow. Pressure and winds are the anchor's missing chapter; the next entry carries what exists.

Air masses.

SSH 0935 Air Masses by Letter Code; The Polar Front

An air mass has uniform moisture and temperature, from a uniform source region. Its code: lowercase m for maritime, moist, or c for continental, dry; uppercase E equatorial, T tropical, P polar, A arctic, so cP is continental polar. At the polar front, sixty to sixty-five degrees north, polar and subtropical air meet. Polar high and subtropical high are the anchor's named pressure cells.

Storms.

SSH 0936 Thunderstorm, Tornado, Tropical Cyclone

A thunderstorm needs warm, moist, unstable air lifted by convection, convergence, orographic uplift or a front, and forty thousand occur a day worldwide. A tornado descends from a supercell's mesocyclone, and about seventy-five percent occur in the United States. A tropical cyclone, hurricane, typhoon or cyclone by basin, has winds over seventy-four miles an hour and an eyewall.

Weather against climate.

SSH 0937 Weather Is Today; Climate Is Thirty Years

Weather is the current state of the atmosphere at a place and time; climate is the statistical average of weather for a location over thirty years or more, NOAA's definition. Weather changes by the minute; climate takes decades, a system of ocean, air, rock, water and life, and the Cretaceous was warm with no polar ice. Historic climates tracked greenhouse gases, the anchor says.

Three entries to close: classifying a climate by Köppen, change on two clocks, and what the climate record shows.

Köppen.

SSH 0938 Köppen: Classifying a Climate by Temperature, Rain, and Season

The exam gives a climate's traits or letter and asks its group, and Dastrup's Köppen classification, based on temperature, amount of precipitation and its timing, with vegetation as the indicator, sorts five groups and one addition. A, tropical: every month averages eighteen degrees Celsius or more, abundant rain, within roughly fifteen to twenty-five degrees of the equator. B, dry: evapotranspiration exceeds precipitation, a moisture deficit, deserts and steppes. C, temperate: the transition between tropical and polar, mild winters, warm summers, plentiful rain. D, continental: Northern Hemisphere only, forty to seventy degrees north, far from large water, four seasons and wide ranges. E, polar: warmest month below ten degrees, bitter winters, dry. H, highland: altitude mimics latitude, added after Köppen. A climate and its plants and animals make a biome. No month below eighteen degrees, rain year-round: A. More evaporation than rain: B. Hot summers, frigid winters, deep inside a large continent: D. The warmest month barely reaching ten degrees, tundra at the treeline: E. Mild wet winters, warm summers: C. Ask temperature first, then whether rain exceeds evaporation, then seasonality. The trap is D in the Southern Hemisphere; the anchor says no landmass there is broad enough. The second trap is B by temperature; dry is defined by the moisture deficit, hot or cold.

Change on two clocks.

SSH 0939 ENSO and the Pleistocene: Change on Two Clocks

The Pleistocene, one point eight million to about ten thousand years ago, cycled glacial and interglacial periods, and ours has run about ten thousand years. ENSO recurs every two to seven years: trade winds weaken or reverse, warm water piles up off South America, and upwelling off Peru ceases, with La Niña as the cold counterpart. Long-term causes are plate tectonics, supercontinents and volcanism.

The anthropogenic signal.

SSH 0940 The Anthropogenic Signal: What the Record Shows and Who Emits

The exam's climate-change item asks what the record shows and what explains it, and the anchor's last chapter answers in a voice the course keeps attributed. The record first. Climate has never been stable over geologic time: the Cretaceous had no polar ice, the Pleistocene swung between glacial and interglacial, and the present interglacial is about ten thousand years old, with sea level up about one hundred twenty-five meters since the last glacial maximum. On shorter clocks, ENSO reshuffles heat across the Pacific every two to seven years, and over millions of years plate motions, supercontinents and volcanism have warmed and cooled the planet. Against that background the anchor sets the present: most of the warming has come since nineteen hundred; the nine warmest years on record, at the anchor's writing, all fell after nineteen ninety-eight; two thousand ten to two thousand twenty was the warmest decade; and sea-level rise, which had settled near zero point seven millimeters a year, began accelerating around eighteen seventy. The explanation second. Dastrup states, citing NOAA and NASA, that the scientific consensus among those who study climate is that the current warming is anthropogenic: more greenhouse gases are trapping heat, and the changes in their concentrations are due to human activity rather than natural processes. The emitters third, voiced with the anchor's own caveat. The United States was long the largest emitter, about twenty percent of the total; China's rapid growth carried its emissions past the United States in two thousand eight; and since the United States has about one-fifth of China's population, the average American produces far more than the average Chinese person. The anchor draws no policy conclusion from that comparison, and neither does the course. Every figure here is the anchor's, dated to its writing and attributed to it and to NOAA and NASA; unit twelve carries the greenhouse effect's magnitude and its check. The record read as pattern, the cause stated as the anchor states it: that is how this unit reads everything.

Look at what you can now do. You can name a fault from whether the hanging wall drops, rises or slides, and you know the origin is the focus below the epicenter. You can say weathering breaks rock and erosion removes it, that water is the principal agent, that the oceans hold ninety-seven percent, and that streams and groundwater move the rest. You can say winds, rotation and basins drive surface currents, and that sea level slowed and then accelerated from about eighteen seventy. You can name latitude as the first control of temperature, read cP as continental polar, and say climate is thirty years of weather. And you can classify a climate by temperature, deficit and season, and state what the record shows with every figure attributed to the anchor and its sources, which is pattern read as process, carried to the end. Unit eleven opens on population.