Sublimation at the lower surface of a seasonal sheet of translucent CO2 ice at high southern latitudes during the Martian spring, and rapid outflow of the CO2 gas generated in this manner through holes in the ice, has been proposed as the origin of dendritic 100 m–1 km scale branched channels known as spiders or araneiforms and dark dust fans deposited on top of the ice. We show that patterns very similar to araneiforms are formed in a Hele-Shaw cell filled with an unconsolidated granular material by slowly deforming the upper wall upward and allowing it to return rapidly to its original position to drive air and entrained particles through a small hole in the upper wall. Straight, braided and quasiperiodic oscillating channels, unlike meandering channels on Earth were also formed