How a Magma Sea Made Upper Peninsula Waterfalls

Please Note: The text below is a lightly-edited transcript of the above video. For the best experience, I recommend watching and/or listening to the video if possible; out of context, the text below may feel sightly disjointed.

So, if somebody were to ask you what you picture when you think of the state of Michigan — well, if you're anything like me, you might think of the city of Detroit, you might think of the city of Flint, you might think of the Great Lakes and the beaches that go with them… but how about waterfalls?

It turns out, the Upper Peninsula of Michigan is just full of waterfalls. (Even a conservative estimate says there are more than 200 of them up here!) So, earlier this month, I took a chill, solo drive to try and go see three of those waterfalls in an afternoon — three that I just kind of randomly picked off a list. And much to my delight, when I got home and started trying to learn more about these falls, I discovered that if you put all three of them together, they tell a story. Specifically, they tell the story of why the western Upper Peninsula in particular has so many waterfalls to begin with.

So, let's go on an adventure! Along the way, we'll see evidence of a gigantic, ancient lava flow; a place where there is a giant crack in the Earth's crust; and of course, we'll learn how you get a waterfall in the first place.

Let's do it.

On this adventure, I set out to see Eagle River Falls, Jacob's Falls, and Haven Falls, all of which are in Michigan's Keweenaw Peninsula. And I didn’t really know what to expect! All I knew was that there were probably some fascinating geology stories out there.

One thing I immediately came across on my drive were huge, dark cliffs along the side of the highway. I knew they were mostly volcanic rock — and that that had a lot to do with why there are just so many waterfalls in this area.

See, the western Upper Peninsula in particular has experienced a ton of volcanic activity. About 1.1 billion years ago, there was this major event called the Midcontinent Rift, where for some reason or another, the Earth's crust literally started to pull apart. That led to an inconceivable amount of lava, and I made a separate video describing the event in more detail. But the key detail for this story is that as all that lava cooled and hardened, it created volcanic rock like basalt. Specifically, it created a big rock layer geologists call the Portage Lake Volcanics.

Over long periods of time, a lot of that volcanic rock got buried by other kinds of rock, like sandstone. But that definitely doesn't mean it's gone — something I learned firsthand at Eagle River Falls…

So, around the time I was in middle school, I learned that waterfalls form through erosion — when water comes along and wears away some kind of rock. But then, I started researching this project, and literally the first thing I that learnedwas that waterfalls can form all kinds of ways. Anything from glacial activity to big faults or cracks in the Earth's crust can do it, and that's something we'll get into more when we go to Haven Falls.

But here, Eagle River Falls did at least partly form through that classic way you might have also learned about in middle school, which is through erosion — although glaciers did definitely help.

This rock at the top of the falls here is that Portage Lake Volcanics layer, which is pretty hard, tough, rock. And the rock at the bottom of the falls is part of the Copper Harbor Formation, or the Copper Harbor Conglomerate, depending on which source you're looking at. (Conglomerate is just a bunch of kind of round-ish rocks cemented together. Here, it's a mix of pieces of lava rock, and also sediments and sedimentary rock carried down from the nearby mountains.)

Over time, as glaciers from the past scraped over this land and this river flowed toward Lake Superior, it wore away the softer conglomerate and left behind this big old cliff of volcanic rock.

Now, geology-wise, though, erosion and glacial activity are definitely not the only things that made waterfalls in the Keweenaw Peninsula. Honestly, I'm not even sure they're the most interesting. Of the three waterfalls I visited on that day, my favorite story is probably the one behind Haven Falls.

But, we'll get to that in a second.

(Aside: I couldn't really find much on the geology of Jacob's Falls. I can tell you that it's another waterfall flowing over the Portage Lake Volcanics, and I can also tell you that there's a pretty cool hiking trail behind it. But that's about it. Still, I wanted to include it [in the video] because it's so quaint and lovely and easy to get to, and I highly recommend a quick stop if you're ever in the area.)

So, I mentioned there are other ways waterfalls have formed in this area. And a big one is through faults.

A fault is a break in the Earth's crust where two pieces of rock have moved past each other somehow. It could mean they slid past each other horizontally, or that one piece of rock got shifted above the other, or something in-between. (If you're familiar with faults already, it might be in the context of earthquakes, since a lot of earthquake activity happens along faults.)

Much to my surprise, it turns out the Keweenaw Peninsula also has a gigantic fault. Appropriately, it's called the Keweenaw Fault, and it cuts basically right down the middle of the peninsula. This fault in particular is called a thrust fault, which means it's a place where one block of rock got... well... thrust... above another one. And they're pretty common in areas of compression.

Now, if you're wondering exactly how the activity on this fault happened... me, too. I read a couple of papers and research summaries about this, but based on other things I know about the area, I have a suspicion that those hypotheses are outdated. So, I haven't included them here.

That said, there are a couple of things we do know about this fault.

One is that it's not active. There's really not activity happening on this fault, so there is no risk of a major earthquake in this area.

And the other thing we know about this fault is that happens to run right through Haven Falls.

One thing I learned is that all the main activity on the Keweenaw Fault happened like, millions of years ago. So, a lot has happened since then. Parts of the fault are buried; other rocks are eroded. It's been a long time.

Another thing that really cleared things up for me is that I watched this truly excellent video by a local geologist, where he pointed out that although we map and model faults as straight lines, they're actually more like gradients. So, while I was filming these clips, I was basically standing on the Keweenaw Fault.

Haven Falls is another place where the water flows over the Portage Lake Volcanics, but what strikes me about it is that the falls don't exist just because the river eroded some rock, or because there were glaciers here. It's also a direct consequence of the Earth's crust just... physically shifting around.

It's the same feeling I got when I lived in Washington, DC for a summer and just wandered around these historic places and could really think about the significant events that had happened there. It's just that here, the significant event was millions and millions and millions of years ago, and involved big pieces of rock.

And that brings me to something I really loved about filming this video. I set out on that Saturday afternoon to just go see three waterfalls because I wanted to explore and see some beautiful things. But then, along the way, I ended up learning a story. I learned how a huge amount of lava a billion years ago created this tough, durable Portage Lake Volcanics layer. And then, over time, as other rock around that layer got eroded, it gave us Eagle River Falls, and Jacob's Falls. And as that rock layer got physically thrust around, it gave us Haven Falls.

The waterfalls are absolutely beautiful in the spring, and if I knew none of that, it still would've been worth going. But it was also just super fun for me to be able to put the falls in context and learn the story of how they got there in the first place.