Hole in the Clouds

Tag: river

Lena's Mouth

Dec 9, 2011

The satellite view of Philadelphia in infrared, from a few days ago, led some people to ask for more false-color imagery of our planet. Here we've got a river delta in the tundra of eastern Siberia, where the River Lena empties into the Arctic Ocean. The image is from mid-summer, when the plants of the tundra were bursting with new growth, thanks to twenty-four hours a day of sunlight. The color scheme here is different from that of the Philadelphia scene but still not closely related to the colors a human eye would detect. The data displayed comes from three sensors on the Landsat satellite: one that detects infrared energy, another that detects near-infrared energy, which is very sensitive to the chemicals associated with growing vegetation, and a third sensor that picks up a part of the visible spectrum. Vegetation is green, exposed rock or soil is pink, wet soil (mud) is purple, and ice is blue.

Even in mid-summer, the sea ice floats close to shore. It will take another month or two for most of the ice to melt and/or wash out to sea, but as soon as it does freezing temperatures will return and ice formation will begin again.

The innumerable ponds and distributary streams are typical of flat places throughout the Arctic tundra, where permafrost just below the surface impairs drainage. Meltwater and rainwater sit on top of the permafrost all summer long, breeding mosquitoes...... which don't show up in the satellite imagery.

birdseye view   Russia   infrared   Siberia   remote sensing   tundra   Landsat   Lena River   delta   river   Arctic Ocean  

Over the Troubled Bridge

Feb 11, 2013

Throughout the winter of 2012, Indonesian schoolchildren went to and from school every day via this damaged suspension bridge, which lost one of its pillars during a flood in January.

"Oh no," thought Djakarta-based photographer, Beawhirta, when he came across this scene. "These could not be children who wanted to go to school. It was more like an acrobatic show, with the collapsed bridge as an apparatus and without any safety device at all. They walked slowly, sometimes screaming as their shoes slipped. Suddenly the rain came."

Even in the rain, all the children made it safely across the Ciberang River, at least on the day of the photo shoot. About three months after the photo gained wide attention in Indonesia, the bridge was repaired.

children   bridge   river   Indonesia   danger   (Image credit: Beawhirta, h/t: K Maldre)  

Season of the Scour

Jul 20, 2013

The Chinese term for what's going on here gets translated as sand-washing, but the operation is really more like sand-blasting. Every summer, just before the rainy season, specialized gates in a dam holding back the Yellow River are opened wide, and the river bursts through under such high pressure that the sand and silt in the river water scour the river bottom for the next 800 km.

The nozzles will be left open for about three weeks, till the water level in the Xiaolangdi Reservoir is low enough to accommodate summer rain and the riverbed downstream has been blasted deep and clean. In its lower reaches, the Yellow River meanders slowly and is prone to silt buildup and flooding. In recent years, sand-washing has been undertaken at least once and usually twice a year.

The photo above shows the sand-washing last week; recent rains had stirred up the sediment in the water, turning it all yellow. The photo below shows the beginning of last summer's sand-washing operation, which took place after a dry spell during which the sediment had precipitated out of the water column and settled to the bottom of the reservoir.

China   (h/t: Cathy Goldwater)   river   dam   flooding   sand-washing   reservoir   Yellow River