Flooding along the Susitna River

Heavy rains and floods struck the Susitna River Valley in south central Alaska in September 2012. The fast-rising waters inundated homes and businesses, washed out roads, and prompted authorities to open shelters, according to news reports. On September 21, the Anchorage Daily News reported that the Susitna River rose so much that it backed up into its tributaries.

These images show the Susitna River Valley where it empties into Cook Inlet. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured the top image on September 30, 2012. MODIS on the Terra satellite captured the bottom image on September 27, 2011. Both images use a combination of visible and infrared light to increase contrast between water and land. Water varies in color from electric blue to navy. Vegetation is bright green. Snow and clouds are pale blue-green.

In September 2012, the Susitna River and its tributaries were visibly swollen, and water rested on floodplains along the rivers. The lighter color of the rivers likely resulted from sediment; during floods, fast-flowing rivers can carry heavy loads of mud and debris.

Besides floods in 2012, other changes were apparent between 2011 and 2012. Compared to the previous year, 2012 showed more intense shades of green, suggesting more robust vegetation. Likewise, snow cover on the surrounding mountains—distinguishable from clouds by its more precise outlines—was more widespread.

The Anchorage Daily News reported that some communities along the Susitna River experienced the worst flooding in 30 years. After the peak of the flooding passed, residents began a lengthy cleanup process, and authorities warned residents to avoid well water until it had been thoroughly tested for contamination.

1. References

2. KTUU. (2012, September 20) Mat-Su floods, road closures: 10 people rescued in Wasilla. Accessed October 2, 2012.
3. Mauer, R., Grove, C. (2012, September 22) Floodwaters recede in Talkeetna. Anchorage Daily News. Accessed October 2, 2012.

NASA Earth Observatory image by Jesse Allen, using data from the Land Atmosphere Near real-time Capability for EOS (LANCE). Caption by Michon Scott.

Instrument: 

Aqua - MODIS