Earth science
Glaciers and sea level
Glacier budget, isostasy, sea level, and glacial deposits.
Basics
Glacier budget
The difference between upper accumulation (snow) and lower ablation (melt, calving) grows or shrinks a glacier. The equilibrium line is that boundary. Ice moves by plastic creep and basal slip. Warm wet coastal glaciers tend to be fast; cold dry ice sheets slower. Measurement is mass and thickness, not only the snout.
Isostasy
Thick ice loads the crust; when it melts the land rises slowly (rebound). Scandinavia and Hudson Bay are examples. Mixing “absolute” sea level with local land motion misreads the tide gauge. Mantle viscosity sets the rebound rate. GPS and raised shorelines help split the signals.
Sea level
Sea level mixes a mass term (land ice to ocean), a steric term (thermal expansion), and local circulation and wind. Mountain glaciers and ice sheets contribute different shares. Basal melt and ice-shelf collapse in Greenland and Antarctica steer the far outlook. This page is a sketch. Use national scenarios for flood numbers.
Glacial deposits
Till is poorly sorted mixed sediment; eskers are sinuous ridges from tunnel streams; drumlins are hills aligned with flow. U-shaped valleys and fjords are cut marks. Shorelines moved a lot after the Last Glacial Maximum. An erratic is a far-travelled boulder. On a map, do not mix glacial symbols with river ones.
Formulas
Mass budget (sketch)
Positive means thickening. Often in metres water equivalent.
Symbols
-
ΔMchange in mass
Thermal expansion (rough)
Layer thickness H, expansivity α. Salinity also changes density.
Symbols
-
αthermal expansivity -
Hlayer thickness
Ice-to-ocean sea level
Melted ice volume over ocean area. Rebound is separate.
Symbols
-
ΔV_iceice volume that entered the ocean -
A_oceanocean area
Key table
| LGM | Last Glacial Maximum ~21 ka; sea level much lower than now |
|---|---|
| Alpine vs ice sheet | alpine glaciers are fast and small; ice sheets dominate sea-level mass |
| Floating shelf | already floating: melt barely raises sea level (Archimedes); land ice behind can speed up |
In this field
Rocks and plate tectonics
Rock cycle, earthquakes, volcanoes, plate boundaries.
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Layers, wind, clouds, fronts.
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Currents, carbon, climate vs weather, relative and absolute age.
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Minerals and Mohs, water cycle, groundwater, soil.
Hazards and resources
Volcanoes, slides, storms; fuels and ores.
Geologic time and carbon
Relative and absolute ages, the carbon cycle.
Weathering, soil, and the water cycle
Weathering, erosion, soil profiles, and the water cycle.
Earth’s magnetic field
The dynamo, the dipole, inclination and declination, paleomagnetism and seafloor stripes.
Groundwater
Porosity, permeability, water table, Darcy, aquifers and aquitards.
Seismic waves
P, S, and surface waves, travel-time curves, magnitude, and Earth’s interior sketch.