What a difference a week can make! This pair of true-color images
acquired by the Moderate-resolution Imaging Spectroradiometer (MODIS) on
satellite show the spring thaw and resulting flooding of
the Lena River, a principal waterway of eastern Siberia. The first
image, acquired on May 22, 2001, shows the Lena as a mostly frozen,
white ribbon running north. An eastward flowing tributary, the Vilyuy,
also appears frozen. In the second image, taken only 8 days later, large
sections of the Lena, as well as the Vilyuy appear to be almost
completely thawed. The formerly white
ribbon of the river now appears decidedly brown, likely indicating
sediment churned up by high water.
The region is experiencing its worst flooding in one hundred years, with
hundreds of thousands of people being affected by the floodwaters that
have resulted from the melting of the snow pack accumulated over a
particularly harsh Siberian winter. Explosives are being detonated in
many places to dislodge huge blocks of ice that are backing up rivers
and exacerbating flooding.
The Lena River is one of the longest rivers in the world. It flows
northeast and then north from its source in the Baikal Mountains south
of the Central Siberian Plateau, and it empties into the Arctic Ocean
via the Laptev Sea. At the mouth of the Lena River is a delta that is
about 250 miles wide. The delta is frozen tundra for about 7 months of
the year, but spring transforms the region into a lush wetland for the
remainder of the year. Part of the area is protected as part of the Lena
Delta Wildlife Reserve.
Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team
In the span of three weeks, spring crept over the Siberian landscape surrounding the northern half of the Lena River. Many of the rivers in Earth’s temperate zones run high in the spring when melting snow and spring rain flood river basins. On the Lena River, however, spring flooding is almost inevitable for another reason: ice. Like other north-flowing rivers, the upper reaches of the Lena melt before their downstream counterparts. Because the northern mouth of the river remains frozen while the southern body of the river flows freely, water naturally builds behind the ice, forming a temporary reservoir that drains as the ice dwindles.