You will never be as big of a nerd as this high school earth science teacher, that you can take comfort in.

That's a sediment trail coming out from the river. The water slows down when it hits that bay dropping the sediment out of its hold.

If you like images like this (and of course have plenty of time to waste. Yeah right, it sucks being a grown up) go to http://www.yannarthusbertrand.com
He takes amazing "Earth-from-above" images!