Geography tricks that make landforms stick

Q: Explain the STMD river sequence — features and processes at each stage.

A: STMD: Source, Tributary, Meander, Delta. Source: where the river originates — spring, glacier melt, lake overflow. Upper course: steep gradient, fast flow, vertical erosion dominates — V-shaped valleys, waterfalls, rapids. Tributaries: smaller streams join the main river, increasing discharge. Middle course: gradient decreases, lateral erosion increases, river begins to meander — wider valley floor, floodplain develops. Meander: characteristic loop in lower course on flat ground. Faster flow on outside of bends causes erosion (river cliff); slower flow on inside causes deposition (point bar). Oxbow lake: meander cut off when river takes shortcut during flood. Delta: where river meets sea — velocity drops, sediment deposited. Types: bird's foot (Mississippi), arcuate (Nile), cuspate (Ebro).

Q: What are the three types of plate boundaries and what landforms does each create?

A: Plate tectonics drives most major landforms. Divergent (plates move apart): Mid-ocean ridges — new seafloor created (Mid-Atlantic Ridge grows 2.5cm per year). Continental rift valleys — East African Rift. Iceland sits on Mid-Atlantic Ridge. Convergent (plates collide): Oceanic-continental: denser oceanic plate subducts, creating ocean trench and volcanic mountain range (Andes, Cascades). Oceanic-oceanic: island arcs with volcanoes (Japan, Aleutians). Continental-continental: no subduction — both buckle upward creating fold mountains (Himalayas — India colliding with Asia, still rising). Transform (plates slide): strike-slip faults, major earthquakes (San Andreas Fault). Ring of Fire: Pacific plate boundaries — 90% of world earthquakes and 75% of volcanoes.

Q: Explain weathering and erosion — mechanical vs chemical weathering with examples.

A: Weathering: in-place breakdown of rock. Mechanical (physical): breaks rock without changing chemistry. Freeze-thaw: water expands 9% when freezing — cracks rock, dominant in high altitude and latitude. Thermal expansion: heating and cooling cycles stress surfaces. Root wedging: plant roots grow into cracks. Salt crystallization: in arid coastal areas. Chemical: changes rock chemistry. Oxidation: iron minerals rust — red soils in tropics. Hydrolysis: water reacts with minerals — feldspar becomes clay. Carbonation: CO2 in rainwater forms carbonic acid — dissolves limestone creating caves, sinkholes, karst landscapes. Chemical weathering faster in hot wet climates. Mechanical weathering dominates in cold dry climates. Erosion: transport by water (most powerful), wind, ice (glaciers — most abrasive), gravity (mass movement — landslides).

Q: What is a watershed and why is watershed management important?

A: Watershed (drainage basin): all land that drains to a common point. Bounded by divides (ridges). Major watersheds: Mississippi (drains most of central North America), Amazon (20% of all river water), Congo, Nile. Continental divides: Rocky Mountain divide separates Pacific from Atlantic and Gulf drainage in North America. Watershed management importance: (1) Water quality — pollution anywhere in watershed reaches the river. Nitrogen and phosphorus from Midwest farms travel down the Mississippi creating a dead zone in the Gulf of Mexico. (2) Flood control — deforestation and urbanization increase runoff and flood risk downstream. (3) Water supply — many cities depend on upland watershed forests for clean water. (4) Ecology — salmon require clean headwaters. Integrated watershed management coordinates all users and activities.

Q: How do glaciers shape landscapes? Compare glacial and river landforms.

A: Glaciers are powerful erosion agents — embedded rock acts like sandpaper. Glacial erosion features: Cirque — bowl-shaped hollow at glacier origin. Arete — knife-edge ridge between two cirques. Horn — pyramidal peak carved by cirques on multiple sides (Matterhorn). U-shaped valley — wide, flat-bottomed with steep sides (Yosemite). Striations — scratches in bedrock showing glacier direction. Hanging valley — tributary glacier left hanging after main glacier eroded deeper, creating waterfall. Glacial deposition features: Moraine — ridge of unsorted debris (till). Drumlin — oval hill shaped by overriding ice. Erratic — boulder transported far from its source rock type. Fjord — U-shaped valley flooded by seawater after glacial retreat. Key contrast: river valleys are V-shaped (vertical erosion); glacial valleys are U-shaped (equal lateral and vertical erosion).