The images provided by the Moderate Resolution Imaging Spectrometer (MODIS) aboard NASA's Terra and Aqua satellites are always spectacular and frequently provide some great perspectives on atmospheric, land, and lake processes over northern Utah.
Yesterday's Aqua overpass below tells us quite a bit about the Great Salt Lake. Note it's limited area, with just a thin sliver of water in Farmington Bay east of Antelope Island and no water at all in most of the Bear River Bay, with the exception of diked and reservoir areas like Willard Bay. Extensive grey areas, indicative of playa, surround the Great Salt Lake and are consistent with it's low elevation. You can also see a large evaporative pond just to the east of Stansbury Island and the contrast in color between the northern and southern half of the lake, which is divided by an earth railroad causeway that runs westward from Promontory Point. With the lake at a relatively low level historically, it is surrounded by extensive grey playa, that helps to illustrate the area of the lake at high-water stands.
 |
| Source: NASA |
 |
| Source: www.utahfireinfo.gov |
Jim - what causes the dramatic color differences south vs north of the railroad causeway? Bob
ReplyDeleteMost of the freshwater comes into the southern half, so there is about a factor of 2-3 difference in salinity between the two halves (south ~9-12%, north ~28%). In turn, this leads to differing algea species in the two halves, which results in the color contrast (warning: this is not my area!). There is some discussion at http://earthobservatory.nasa.gov/IOTD/view.php?id=7857.
DeleteJim
PS: I should have addressed this in the original post!
Jim - thanks for the response. Visually the difference is very distinct. Does the lake surface temperature differ for the two halves? Has the causeway been there since the Transcontinental Railroad? Bob
DeleteI haven't noticed a huge difference in temperature between the two halves in AVHRR imagery. The causeway was built in 1959. THe original transcontinental railroad went around the north end of the lake, with the golden spike laid very near the lake. You can still see the old railroad grade. More info at www.nps.gov/gosp/index.html. Steven Ambrose's book Nothing Like It in the World is a really great account of the building of the railroad and one of my favorite historical books.
DeleteThat's an amazing picture. Does the lake level vary seasonally, or is it more dependent on fluctuations in average rainfall from year to year?
ReplyDeleteYes, it varies seasonally. There is a graph at http://www.gslyc.org/weather/gsl_highs_and_lows.html showing the long-term lake elevations back to 1980 that illustrates the seasonal fluctuations (typically ~2-3 feet) and longer term elevation variations. Larger seasonal increases can be produced during big snow/runoff years. The seasonal declines, however, are generally more consistent from year to year (although there are variations).
DeleteJim