Cliff Formation for Dummies

Cliff and bench differential erosion

One of our staffers claims a partner who is "The world's oldest fifth-grader." No, she isn't still in elementary school: the affectionate nickname refers to her love of learning elementary facts about everything that fascinates kids when they're about ten years old. With that description in mind, we took a look at "How Cliffs Are Formed," a Gregory Hamel post at Sciencing.com.¹ We figured that a "question" like that pretty much deserved an answer at the fifth-grade level...

Hamel parlayed his economics BA into a mishmash of science fact and science folly at the old eHow.com, beginning with an inane definition of a cliff:

"Cliffs are steep formations of rock that occur frequently in nature along coasts, riverbeds and in mountainous regions."

The staff geologist was heard to mutter, "Gaaaah! Another idiot who misuses 'formation'!" That, however, was not the least of his complaints with Gregory's steaming pile of scientific bull. Hamel went on to explain plate tectonics:

"Underneath the ground, the earth consists of large tectonic plates that shift around over time. When two of these plates meet, extreme pressure is created which sometimes forces one or both of the plates upwards over time. This can result in the creation of mountains and cliffs. "

Uhhh, yeah, Greg. Tectonics creates cliffs... Hamel also lays cliff formation at the feet of water and erosion:

"...the repeated lapping of water against rocks as waves gradually wears the rock down, which can form cliffs... rivers and gullies that swell with rain water gradually cut into the earth as they flow, which can create cliff walls on either side..."

Sure, Greg. And he also blames glaciers:

"Another cause of the formation of cliffs were the glaciers that once covered much of the earth during the ice age. When the glaciers slowly moved across the earth, their tremendous weight ground out depressions in certain areas creating cliffs much like a river would. The difference is that glaciers are extremely expansive so the cliffs they form can cover large areas instead of being confined to a certain, path like a river."

We aren't really sure what those cliffs that "cover large areas" are: moraines, perhaps? Of course, most fifth-graders know that Hamel's conflated continental and alpine glaciers here... But what people who actually know jack about cliffs will tell you is that Gregory danced all around the facts without actually getting to the point. The point Hamel should have addressed was clearly stated in one of his references:

"...hard rocks form steep cliffs and soft rocks and badly broken/fractured rocks form more gently sloping cliffs..."

Yup, Greg, you blew it by never mentioning differential erosion. Then again, you probably forgot about that from your fifth-grade earth science lessons and took astronomy or weather instead of rocks for jocks as your science elective at St. Olaf's. Well, don't worry: you still qualify for an award: you've won the Dumbass of the Day.

¹ The original has been sent to the rewrite team by Leaf Group (we'll get to that travesty later), but can still be accessed using the Wayback machine at archive.org. Its URL was   sciencing.com/cliffs-formed-5120524.html

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