Wind-exposed layers

Wind-exposed layers
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On Earth, layers comprising the geological record of an area are most often exposed by fluvial erosion, as a river cuts through rock (a typical example is the Grand Canyon). On Mars, fluvial channels are not so common (especially in the past few billion years). But the wind has relentlessly worked away at the surface,

Overhang

A Piece of Mars: There’s a fabric of erosion in this 1×1 km (0.62×0.62 mi) scene, with the main wind blowing from lower right to upper left (and if you look carefully you’ll see there’s a second, subtler fabric a bit clockwise from that one). The result is a landscape strewn with streamlined rock called

Just do it

A Piece of Mars: It’s all about wind scour here in this 0.75×0.75 km (0.47×0.47 mi) view. The big “swoop” is an erosional channel dug into the surface by winds (blowing from the lower left) trying to erode the hills in the center. But notice that the hills are all aligned to the upper left/lower

Cross-strata or not?

A Piece of Mars: Sand dunes are one of the few sedimentary phenomena that leave behind layers that aren’t horizontal. They tend to have a characteristic lean to them (and we call them cross-strata). So when I see something that looks like tilted layers on Mars, I take notice. This 0.625×0.5 km (0.39×0.31 mi) scene

Dunes carving up rock (3D)

A Piece of Mars: Get out your 3D blue/red glasses (or look here for a 2D version if you can’t find them). This is a 3.2×1.8 km (2×1.13 mi) scene showing dark dunes carving lanes 50-70 m (165-230 ft) deep into a stack of brighter sedimentary layers. Over time, the sand wears down the rock

On Mars the wind carves stream channels

A Piece of Mars: This 1.6×2 km (1×1.24 mi) scene mostly shows what wind will do to fine-grained, weakly-consolidated surfaces. It has created topography that further strengthens wind scour in the hollows, which even leave kilometers-long grooves reminiscent of water-carved streams. If this were Earth I’d guess they had been carved by water first. But

Windblown: ancient and recent

A Piece of Mars: HiRISE is celebrating 10 years of success by showcasing its first high resolution image, taken back in 2006. Here is a portion of it, shown at 1/4 the full resolution (the scene is 2.5×2.5 km across). I highly recommend downloading the HiRISE image viewer and looking at the whole thing, it’s

Erosional remnants

A Piece of Mars: The erosionally-streamlined bright areas are on high ground. They are remnants of a vast dusty mantle that once covered this whole area – the rest of it has been blown away. The surrounding regions (check out the whole image) are still covered by that mantle, but here you can see through

A light touch

A Piece of Mars: This 3.2×1.8 km (2×1.1 mi) area shows terrain covered by bright dust. Dark stripes are areas where wind has lightly scoured the surface, revealing the dark material beneath. Faint bright lines criss-cross the surface – these are tracks left by dust devils. The dust devils disturb the surface but don’t lift