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The Waterfall (or "Wowterfall") Period is one of the periods of the xkcd comic Time, within the Mountain Era.
It lasted from frame 1929 to 1969.

"Wowterfall" is a portmanteau of "Wow" (the word used by Cuegan to describe the scene) and "waterfall," originally coined by fhorn on the One True Thread.


The period begins with Megan leading Cueball to see the discovery she made at the end of the previous period, by following the tiny river in the direction toward the viewer, thus stepping through a total of 3

GIF of the stunning 4-frame "Wowterfall" sequence.

3D-slices (including the terminals) as she shows him where it leads. When they pause at the third slice, Cueball says, "Wow." The camera angle is then turned 90 degrees and zoomed out significantly to show Cuegan in profile standing at the top of a tall waterfall (approximately 24.4 q high, or about 42.75m / 140ft). The waterfall is shown for 4 frames, creating one of the most stunning visual sequences of the comic to this point.

The perspective turns back to Cue and Megan face on, and they stand at the top of the falls discussing it. Cueball remarks that the land rises while the river doesn't (basically a crude definition of a canyon) and Megan corrects him to say that the river has gone up to, just not at the same rate. They question how water could wear away rock to form a canyon and conclude that it must take a very long time, but that it helps that the stone of the area seems to be particularly "crumbly" and "sandy" according to Cueball, after he picks up a rock and examines it.

They next wonder how deep it gets and hypothesize that it might be as deep as the mountain is tall. The antecedant for the pronoun "it" which Cueball uses here is admittedly vague (see discussion section below). Megan responds that it could actually be deeper, as they can't tell how deep the water goes. However, Cueball points out that it can't be much deeper than the surface of the sea, or else it wouldn't flow very fast, and if it didn't flow fast, it probably couldn't carve out a canyon. Megan agrees, but does still wonder how rivers manage to cut all the way through mountains in the first place, wondering aloud how such a process begins. She then looks to the right of the frame (the direction of their journey) and wonders what the top of a mountain is like. Cueball says, "Let's find out." They turn around and return through the 3D slices to retrieve their bags and continue on.


This period continued the discussion of Cuegan's background and apparent naivete about the world. Some continued to theorize, as has been postulated before, that they are either children, or completely foreign to the world they find themselves in. Alternatively, some have suggested that they are actually quite bright, but speak in simplified terms for the benefit of the audience, to feed them critical additional details not relayed by the simple silhouette pictures, or else to make them truly think. For example, their discussion on water carving a canyon ends with Megan's open-ended question about how such a process even begins, perhaps intended to prompt the viewer to contemplate the miracle and complexity of the birth of a canyon.

Pronoun ConfusionEdit

A lot of Cuegan's discussion employs rather vague and repetitive pronouns which led to some abiguity as to when they are talking about the canyon depth versus the river depth. BlitzGirl posited to following "translation" of their dialogue, substituting what seem to be the best antecedants for the pronouns, as well as several other "creative license" modifications for clarification:

Original DialogueEdit

Cueball: I guess the land goes up, but the River stays at the same level.

Megan: The River has been going up, too. But not as fast as the land. Can water really wear away rock like this?

Cueball: I guess it can.

Megan: I can't imagine how long it must have taken.

Cueball: Yeah... *picks up rock* A lot of these rocks are pretty crumbly. Even down there, between all the big rocks, the cliff walls look sandy. Water eats away sand pretty fast.

Megan: Yeah. *Cueball drops rock, they watch it fall* I wonder how deep it gets.

Cueball: Maybe it goes right through the mountain, and it's as deep as the mountain is tall.

Megan: It could be even deeper. We don't know how far down the water goes.

Cueball: Hmm. I guess it can't be much deeper than the surface of the Sea. If it were, it wouldn't flow fast and cut into the ground.

Megan: Oh. Yeah. But then, a River couldn't cut all the way through a mountain, either. Because how would it get started?

BlitzGirl TranslationEdit

Cueball: The land rises in elevation, but the River doesn't. It seems to be at around the same elevation it was when we first saw it.

Megan: The River has been rising in elevation, too, but not as quickly as the land has been rising in elevation. Can water erode rock like this?

Cueball: Apparently so.

Megan: It must have taken a long Time.

Cueball: The rocks are pretty soft, and probably easy to erode.

Megan: I wonder how deep the canyon gets.

Cueball: Perhaps the canyon goes right through the mountain. In which case, the canyon would be as deep as the mountain is tall.

Megan: The canyon could be even deeper if you include the depth of the River.

Cueball: The canyon can't go much deeper than Sea level, though. If it were deeper than Sea level, the water in the River wouldn't have as much potential energy, and would not be flowing as rapidly as it is. It also would not have to erode the land to get down to Sea level.

Megan: Sure. But how could a canyon form in the middle of a mountain? Rivers choose the path of least resistance, and flow through lower elevations. Why would it try cutting straight through a mountain?

Molpy SightingsEdit

There are no known molpy sightings during this period.

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