Earlier Anne posted a bizarre delta-upon-delta image from Lake Athabasca in northern Saskatchewan. Having finished most of my RSS stuff, I followed the flash earth link and started exploring. Oh, my. Lots to see in the region. In addition to Anne's delta the Athabasca River also has a delta into the same lake that's pretty strange looking (picture #1). Backing out a bit, it looks as if the Peace River drained into Lake Athabasca in the not-too-distant past as well, but that it now bypasses the lake and simply joins the outflow downstream (picture #2). (Flash Earth link for the AR-PR delta complex) My guess here is that the coalescence of the AR and PR deltas blocked the western end of the lake, raising the level there, and created a steeper gradient to the east. According to Wikipedia, the major outflow of the lake is Rivière des Rochers. The confluence of that stream with the Peace River marks the beginning of the Slave River.

Before we leave Lake Athabasca, though, and harking back to last month's theme, another interesting bit gleaned from the wikilink above was this: "The Lake Athabasca Sand Dunes, the largest active sand dunes in the world north of 58°, are adjacent to the southern shore. After a long struggle with government bureaucracy and opposition from mining companies, the dunes were designated a "Provincial Wilderness Park" in 1992." (picture #3)

So where does the Slave River go? Great Slave Lake. And another lovely delta (picture #4). So is that the end of the line? Nope... The Great Slave Lake is drained by the McKenzie River, which is the first delta I posted this month. We tend to think of deltas as the end of the line for drainages, but there have been a number of examples this month of stream systems with two or more deltas along their lengths. So here we have an example of a system with at least four significant deltas upstream of the terminal one... and I haven't even mentioned the Hay River delta.