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The state and national borders that had been historically dictated by a river's path mayÌýcome into questionÌýwhen that river changes direction. ÌýCU Boulder Geology Professor Dr. GregÌýTucker understands this issue all too well. ÌýTucker explains that,Ìý"Rivers and streams often appear to be fixed and more or less permanent featuresÌýof the natural landscape. ÌýYet asÌýthe recent [September 2013] flooding in Boulder illustrates, they are often quite dynamic." ÌýIndeed, as a drive up US 36 will quickly tell you, the St. Vrain River now runs in different places than it did just a year ago before the Fall 2013 flooding, which left a lasting impact on the surrounding community.

In 2013, Tucker received an ASSETT Development Award to create an animation about a changing river system.ÌýÌý"I used the ... award to hire a professional scientific illustrator to work with me toÌýcreate a short animated movie depicting river meandering." ÌýThe illustrator is Dr. Cheryl McCutchan of .ÌýMcCutchan made the river animationÌýin Adobe Flash. ÌýWatch itÌýhere:

[video:https://youtu.be/giimXp1dx5U]

Tucker says, "The animation illustrates the way a river can carve a floodplainÌýby eroding and widening the valleyÌýthroughÌýtime." ÌýThe white along the river in the animation represents,Ìý"... Point bars ... fresh sediment ... that grow outward over time," he says. ÌýThe darker green along the river represents the older flood plain. ÌýTucker explains that, "The meandering process leads to fascinating patterns in river valleys, with the channel following a convoluted path that winds back and forth across its valley, and with striking features such as long, curving lakes known as oxbow lakes." ÌýOxbow lakes form when a river floods and changes to a straighter direction, leaving fresh new shoreline between the new straighter riverÌýand the former curve of the river, now an isolated lake in the shape of the letter U, or an oxbow.

Why Use Animation, and How?

Tucker and McCutchan explain that animation can better illustrate changes to a landscape over timeÌýthan wouldÌýjust looking at static images in a textbook. ÌýTucker says, "By creating an animated movie of a hypothetical meandering stream as it evolves over time, creates channel cutoffs, and forms oxbow lakes, we provide students with a means of visualizing the dynamics at play." ÌýMcCutchan agrees:

Illustrations that show three points in the formation of a stream meander or ox bow lake don't give students a sense of how these structures form. ÌýOur goal was to animate the evolution of a stream channel over several millennia as the channel widened ....

However, the animation was not created overnight. ÌýTucker says that the process took about a year to complete. ÌýHe found aÌýcomputer simulation that a Post-DoctoralÌýstudent had writtenÌýseveral yearsÌýprior. ÌýTucker shared the simulationÌýwith McCutchan to give her specificÌýinformation about exactly what happens when a river changes course. ÌýTucker says:

Starting with these images, together with photographs, maps, and satellite images of real meandering rivers, [McCutchan]Ìýused the Adobe flashÌýanimation program to create a series of animation frames that show a river in the context of its valley and floodplain.

McCutchan explains that she chose Flash intentionally because it can create transition between a few frames to convey the illusion of continuous flow of movement: "Flash is an incredibly powerful program that allows the animator to draw only a few key frames. ÌýFlash then interpolates how the objects change between those two scenes ..."

Tucker ultimately intended to show the animation to hisÌýIntroductory Geology students because, "One of the challenges in teaching Introductory Geology is helping people appreciate that the Earth is always changing," but that changing process is often, "slow and intermittent," over hundreds or thousands of years. ÌýHeÌýwants his students to walk away from his Introductory GeologyÌýcourse with some practical knowledge about changing landscapesÌýand, "Have them leave the courseÌýappreciating that change is normal in river systems, so that when theyÌýgo out and buy a house, they appreciateÌýwhat it means to be on a floodplain."

TuckerÌýplansÌýto share this animation on the , whichÌýis a National Science Foundation-funded site that offersÌýshare-able scientific images and animations to the public. ÌýAfter all, he says, "As a scientific community, we should be sharing [information]."

Next, McCutchan and Tucker are planning toÌýcollaborate on a second animation that would use aÌýcross sectional view toÌýshow how river sediment changes over time.