Fanning outWhen channels eroded into mountain ranges cross a boundary and expand onto open plains, t

Fanning outWhen channels eroded into mountain ranges cross a boundary and expand onto open plains, the streams in them tend to spread out into wide features known as alluvial fans. This fan is found on the southern side of the Taklamakan Desert in China, where streams from the Tibetan Plateau spread out into the basin below. Flow happens only occasionally in streams like this, often taking the form of flash floods. When a major rain event happens upstream, the rain coming out of the channel picks a path towards the low ground and that path changes basically every time. The active flow heads to low ground, deposits sediment on its way that can block that channel or change the topography, and then the next time the fan becomes active the water finds a different route to the base. Thus, an alluvial fan builds up as a pile of sediment spreading out in all directions from the central point – where the channel enters the basin.This image was taken by the ASTER instrument on NASA’s Terra Satellite – a multispectral imaging instrument capable of measuring light at a number of different wavelengths between the visible and the infrared. Different surfaces on Earth absorb light at different wavelengths, so measuring the amount of light reflecting off the surface at different wavelengths gives information about what is there. The blue color here has been tuned to a wavelength where vegetation is present – therefore, the blue light tracks a channel system where plants were able to grow. Plant growth, of course, requires water, so this image therefore shows which channels were active during the most recent rain event on this channel. That instrument has been flying for nearly 20 years, building up a database that can let scientists see how these features evolve over two decades.-JBBImage credit: NASA/GSFChttps://flic.kr/p/7HeRA7Instrument:https://asterweb.jpl.nasa.gov/instrument.asp -- source link

More pics about