Rivers of Ice
Glaciers are rivers of ice that flow under their own weight. Unlike water rivers driven by pressure gradients, glacier flow is a slow-motion creep driven by gravity acting on enormous ice masses. A typical valley glacier moves meters per year — imperceptibly slow to the eye, but over centuries it carves U-shaped valleys, deposits moraines, and reshapes entire landscapes. Understanding glacier flow is essential for predicting how ice sheets will respond to climate warming.
Glen's Flow Law
Ice deforms as a non-Newtonian fluid described by Glen's flow law: the strain rate is proportional to the shear stress raised to the power n≈3. This nonlinearity has profound consequences — doubling the stress increases flow rate eightfold. The rate parameter A depends exponentially on temperature through the Arrhenius equation, making warm ice near the melting point flow roughly 1,000 times faster than ice at -40°C. This simulation lets you explore how thickness, slope, and temperature interact to determine glacier velocity.
Basal Sliding and Water
Beneath many glaciers lies a thin layer of water at the pressure melting point. This water lubricates the bed, allowing basal sliding that can exceed internal deformation as the dominant flow mechanism. Subglacial water pressure is the key control: when water pressure approaches ice overburden pressure, the effective friction drops dramatically. Seasonal meltwater pulses reaching the bed through moulins explain why glaciers accelerate in summer — and why increasing surface melt under climate change may destabilize ice sheets.
Ice Streams and Fast Flow
Ice streams are corridors of fast-flowing ice within ice sheets, moving 100–1,000 m/year compared to surrounding ice at 1–10 m/year. They drain the majority of ice from Antarctica and Greenland. Their speed is controlled primarily by basal conditions: soft, water-saturated sediment beneath allows rapid sliding. Ice stream dynamics are the largest source of uncertainty in sea level rise projections because their behavior can change abruptly and is difficult to model accurately.