Full Definition

Aa (pronounced "ah-ah") is a type of basaltic lava characterized by a rough, jagged, clinkery surface made of broken lava blocks called "clinkers." The term comes from Hawaiian—describing the pain of walking barefoot on this sharp surface. Aa forms when viscous or cooler lava flows slowly, causing the solidifying crust to fracture into angular fragments.

Full Definition

Ablation includes all processes removing snow, ice, or water from a glacier: melting (most common), sublimation (ice→vapor), calving (icebergs breaking off), and wind erosion. The ablation zone is the lower glacier where annual loss exceeds accumulation. Climate change has dramatically accelerated ablation worldwide.

Full Definition

Abrasion is mechanical rock wearing through friction from particles carried by wind, water, ice, or gravity—like natural sandpaper. Types: glacial (striations), fluvial (river smoothing), aeolian (desert shaping), coastal (wave action).

Total mass of water vapor in air (g/m³). Independent of temperature. At 30°C air holds ~30g/m³; at 0°C only ~5g/m³.

Exact position using coordinates. Example: NYC = 40.7128°N, 74.0060°W. Uses latitude (N/S of equator) and longitude (E/W of Prime Meridian).

Extremely flat ocean regions at 3,000-6,000m depth. Covered by sediment burying underlying topography. Cover ~40% of ocean floor.

Ocean layer 4,000-6,000m. Complete darkness, 2-4°C, 400-600 atm pressure. Home to bioluminescent creatures. Covers 83% of ocean area.

Growth via accumulation: coastal (beach grows seaward), tectonic (continents grow), planetary (Earth formed from space debris). Opposite of erosion.

Precipitation with elevated acidity (pH<5.6) from sulfur dioxide and nitrogen oxides mixing with atmospheric water. Damages forests, lakes, buildings.

Volcano that erupted during Holocene (last 10,000 years) and may erupt again. ~1,500 active worldwide; 50-70 erupt yearly. Examples: Kilauea, Etna, Stromboli.