Where does avalanche collide?

The rapid downslope movement of a mass of snow, ice, and entrained debris once a slope's snowpack fails: this is the mountain hazard that the word originally named in the Alps. Coaz's 1881 Die Lawinen der Schweizeralpen compiled one of the first systematic registers of Swiss avalanches and their release conditions, and Schweizer, Jamieson, and Schneebeli's 2003 review Snow avalanche formation set out the modern account of how a layered snowpack fractures and releases. The referent is a moving body of snow on a mountainside, described by its volume, speed, and runout, and it shares nothing with a burst of charge carriers in silicon, a property of a cipher, or a cascade of firing neurons beyond the common image of something building and then rushing.[1][2]

Unit

One release event, scaled by snow volume, flow speed, and runout distance

Recovery means

Not applicable

Measured by

Recorded by release area and volume, flow speed, runout distance, and impact pressure in the field and in test chutes

A self-multiplying cascade of charge carriers that sets in when a strong electric field accelerates electrons enough to ionise more carriers by collision, so the current climbs steeply above a threshold voltage. McKay's 1954 Avalanche Breakdown in Silicon established this meaning for semiconductors and described how the multiplied current begins above a breakdown field. The multiplying-by-collision mechanism it names traces back to J. S. Townsend's work on ionisation in gases in the early 1900s, which is why the gas-discharge version is still called the Townsend avalanche. The referent is an electrical process inside a gas or a solid, quantified by a multiplication factor and a breakdown voltage, and it is unrelated to a sliding mass of snow, a diffusion property of a cipher, or a burst of neural firing.[3]

Unit

One multiplication event in a device, scaled by the carrier multiplication factor

Recovery means

Not applicable

Measured by

Quantified by the carrier multiplication factor, the breakdown voltage, and reverse current plotted against applied field

Feistel's 1973 Cryptography and Computer Privacy named the avalanche effect: the property of a good cipher or hash by which flipping a single input bit changes about half of the output bits, so a tiny input change spreads through the whole result. Webster and Tavares's 1985 On the Design of S-Boxes tightened it into the strict avalanche criterion, requiring each output bit to change with probability one half whenever any single input bit is flipped. The referent is a measurable diffusion property of a mathematical transformation, tested by counting flipped output bits over many input changes, not a mass of snow, a current inside silicon, or a cascade of neurons.[4][5]

Unit

One input-to-output mapping, scaled by the fraction of output bits that flip

Recovery means

Not applicable

Measured by

Estimated by flipping input bits one at a time and counting the changed output bits, with about one half taken as ideal

Beggs and Plenz's 2003 Neuronal avalanches in neocortical circuits coined the neuronal avalanche: a burst of propagating activity across a cortical network whose size and duration follow power laws, with no typical scale, read as a signature of a network poised near a critical point. The referent is a cascade of firing captured on multielectrode arrays and summarised by the exponent of its size distribution. It is a statistical pattern of neural activity, not a mass of snow on a slope, a runaway current in a semiconductor, or a bit-diffusion property of a cipher.[6]

Unit

One cascade of activity, scaled by the number of electrodes or neurons it spans

Recovery means

Not applicable

Measured by

Detected on multielectrode arrays and summarised by the power-law exponent of avalanche size and duration