Hello and welcome to Wolf Ridge and the
North Shore. My name is Caroline my name
is Robby and we will 
be your naturalist today as we
explore geology. Can't see a lot from the
desk though, let's take a look around.
Ooo a brown one. Carol look what I found!
It's just a rock. Just a rock?! No, it's an
agate. Agate?
That's a cute pet rock name. Caroline,
it's an agate. It's one of the most
beautiful rocks in all of Minnesota. It's
got these pretty lines on it and this
one's huge!
Well I guess that's pretty cool, but I
don't really get why agates are so
special. Agates are sedimentary rocks.
They form inside the holes of other
rocks. How doe those wholes form? Lake Superior agates form inside basalt and
rhyolite bedrock. Basalt and rhyolite are
igneous rocks that form when the lava
cools and hardens. Just like when you
pour a can of soda and there's bubbles
inside of it, the basalt and rhyolite
also have bubbles inside of them. When
the lava hardens, the bubbles are trapped
inside of the rock. And over time water
will flow through these different areas
and deposit minerals and layer after
layer which gives the agates their
characteristic pattern. Agates are the
state gemstone of Minnesota and you can
find them all over the state. Wow, agates
are pretty cool. I also heard you mention
igneous and sedimentary rocks, are they
called that because of how they're
formed? Exactly. Is there a third type of
rock? Yes, metamorphic and those three will complete the rock cycle. So we've got our
three types of rock. We've got igneous,
sedimentary, and metamorphic rock. And the
important thing to remember is that
they're all named after the processes
that form them and all the rocks can
change from one form to another. Igneous
rock, also known as volcanic rock, forms
from cooling lava and magma. Most of the
features around here on the North Shore,
like palisade head and shovel point, are
all igneous rock. Sedimentary rocks are
formed by lots of layers of sediment.
Little pieces of rocks or sand, and these
are compacted together to form a rock.
Sedimentary rocks are
formed on or near the Earth's surface
from lots of pieces of sediment that are
getting pressed together. Those pieces
are formed by larger rocks getting
eroded, so rain or snow hitting them and
breaking them apart into smaller pieces
and then those smaller pieces get built
back up into rocks. When heat and
pressure are added, the minerals can melt
slightly and rearrange and form a new
metamorphic rock. This happens when the
rocks get buried deep within the earth
and the pressure from all the weight on
top and the heat from the core of the
earth coming up melt it and pressurize
it into that new metamorphic rock. A good
example of pressure creating heat is
when you put your hands together and rub
them really quickly and they start to
warm up.
Wow, those rocks are so cool! I wish I
could see them all. Yeah, they're pretty
awesome and I bet if we call our expert
she can show us around. Hi Carrie! Hi
Caroline, hi Robby! How are you guys
today? What are you up to? We're good.
Robby and I are looking at igneous,
sedimentary, and metamorphic rock and we were hoping that you could help us. Oh,
I'd love to talk rocks! I'd love to!
That's amazing! Where can we meet you?
How about Sugarloaf? I'm sitting right here
on the beach, it's gorgeous. Come on up.
Oh, sounds good that's so close! See you soon.
Hey Carrie, good to see you. Good to see you Robby! Hi Caroline! Hey I'm going to
go out to Sugarloaf. The point out there has
got some amazing things to look at for
geologists and I love to look at rocks.
I've studied them for a while you want
to join me? Absolutely. One thing I want you to know,
is that we're on a scientific and
natural area for Minnesota State. It's
the most protected level of land in the
state. They protect this so we can come out
here and learn about really unique
features unique features. The unique features at Sugarloaf are
all about geology, which is perfect! But
that also means we can't take rocks with
us and we need to leave them there. Here
we are, looking at the igneous rocks
along the North Shore. And you can see
all these layers going back and forth
and we want to figure out how do those
igneous rocks come to be? What are
igneous rocks even made of?
And how do they make layers like that? So,
let's go farther out on the point and
there's some really cool stuff to see.
Here we are with some really cool signs
of the igneous rock layers here. If you
look at this, can you see the distinctive
sorts of shapes and textures and colors
going on? Let's look closer those. So,
if we look right here this rope is sort
of the stuff, this is the top of one of
the lava flows. So as the lava came out
it was moving fast and it was really
thin, which makes it kind of rippley
looking like it's frozen in a rippley-solid form. Right beneath that, see all
these white dots? It's kind of like the
foam in the pop, foam all rises to the
top. So this is the top of one lava flow.
Pahoehoe and then the vesicular layer. If
we look at this one, we're actually
looking not at the top of a lava flow
but at a lava flow that came in
right on top of this one. And it might
have been thousands of years later. They
say about 15 to 17 million years
these lava flows were going on top of
one another but eventually this one came
through. So here comes the lava and as it
hits this layer there's enough gas in
there that bubbles shoot up. Do you see
these tracks? These pipe amygdules are a
sign of the bottom of a lava flow. And
then you get to a place where there's
really no bubbles. Because these stopped
moving they ran out of gas and the bumpy
layers would be up here, and then the pahoehoe. The bumpy layers, or the pahoehoe, are all kind of crumbly and they've washed away in the waves.
So, now we just have this massive layer
and the pipe amygdules before we get
to the next one. Lava flows around here
come from what's called the mid-
continental rift. You can imagine these foam blocks being part of the crust of the
Earth. Kind of floating on the magma down
farther, which of course becomes lava
later, that rift means as a parting of
the crust and as that crust part some of
the lava flows up to the top just like
the waters flowing on top of this. Those
layers harden and that becomes the stuff
that we see all up and down the shore here.
Look at this huge massive basalt flow
and then look underneath it there's
something really different. What's going
on? This looks like a whole different
kind of rock and it sheds into layers.
Look at all these layers and they're all
parallel to each other. That's a real
sign of sedimentary rock. One of the
reasons I think this is probably from a
lake bed, is because it's all the same.
Sometimes layers are kind of crisscross
like this, that's called cross bedding but
this looks like a lake bottom. In this
sandstone you can see layer after layer
so the river came in and deposited more
sand it just went on top of everything.
That's one of the main principles of
geology is superposition: things on top
are younger than the things underneath
them. But that means this basalt is
younger than the sandstone. How can that
be? Well, we've got 15 million years of
the rift with lava flows and in between
maybe some of that erosion down to
sandstone like this rare formation here.
We just walked up cut face creek, which
is in the midst of all that sedimentary
rock, and look at some of the things
we're seeing here. Some of these rocks
have ripples doesn't look familiar? We
can open some of them up, sometimes it
can break the layers open. My gosh look
at this! Look at that! They look just like
the ripples and the lakes that we see
today
even though this rock is probably a
billion years old,
same things that are happening
geologically then are still happening
now. Our final location on the rock tour
is an Ely where we can find a really
famous example of some old metamorphic
rock, Ely greenstone. Ely greenstone was
originally formed about 2.7 billion
years ago and it was basalt underneath
the shallow sea.
Well you might wonder how we know those
things, because it doesn't look like
basalt does it? It's got sort of a stripy
look and it's different colors and also
how do we know what's under a shallow
sea? We know that because of the way that
the Ely greenstone shows up in the land.
You know, kind of that where rocks are
made and we see them where they were
made we could learn a little bit about
the story. So this is kind of like we see
in Hawaii sometimes. Lava that's hitting
underwater cools quickly on the outside
and kind of a pillowy shape and then
as the pressure of the lava comes down,
it breaks open the pillow and goes out
that blob forms another pillow and that
happens over and over again. So this
pillowed
Ely greenstone is a result of that 2.7
billion years ago.
Pretty cool stuff. And then it changed
over time. Things were added on top,
remembered newer stuff gets out on top
of older rock, and eventually there's so
much pressure on that Ely
basalt at that time, that it changes and
the chemicals kind of rearranged and it
makes that metamorphic rock Ely
greenstone. Because of everything that
was covering this old rock, which we
don't know how much that was, but it had
to be eroded away again before it could
show up at the surface. The metamorphic
rock in Minnesota is all really old for
instance that Ely greenstone is 2.7
billion years old. Well there's
some that's even older down in Morton
Minnesota. Morton Gneiss. 3.6 billion years
old, probably part of the original
continent crust.
Just to summarize, igneous rocks are
formed from lava that's cooled down.
Metamorphic rocks are made by heat and
pressure changing the rocks, and
sedimentary are formed by erosion and
all those layers compacting. And now that
you all know how to identify these
different types of rocks, Caroline and I
would like to challenge you to go out
and explore your hometown. Find a local
gravel pit or a cliff, and try to
identify what different types of rocks
there are there. This week for your
nature journal, you could make a diagram
of the rock cycle in your journal; you
could find rocks near you and classify
them as igneous, metamorphic, and
sedimentary; maybe you notice the
landscape and make speculations about
what type of bedrock you're standing on
and if it's hard or soft. I'd also
encourage you this week to try something
new and your nature journal. I tend to
really go for pencil drawings, so this
week I decided to try watercolor
paintings of rocks. It's sometimes kind
of fun to try something new!
Today we've been exploring specific rock
formations at Crystal Cove, Sugarloaf and
Cut Face, and also Ely. Now, we're at Wolf
Ridge at Marshall mountain. It's time to
zoom out a little bit and look at the
whole landscape and see how geology has
played a role in shaping the hills and
mountains. Landscapes are changed either
through deposition, the build-up of new
rocks; or erosion, like we see here the
breakdown of old rocks. One of the
biggest changes in Minnesota
geologically, was the last ice age. During
the last ice age Minnesota was covered
in glaciers which are massive sheets of
ice up to a mile thick in places and
they actually moved across the landscape.
As the glaciers get more ice deposited
on top of them, they get heavier and
heavier until they begin to move. They
then slide across the landscape acting
like a large bulldozer. This is called
scouring. And the ice acts like a piece
of sandpaper rubbing across and
smoothing the ground, but just like
sandpaper the ice has a different effect
depending on how hard the rocks are. This
causes different rocks to be smoothed
away to nothing while other harder rocks
are left behind. This process is called
differential erosion and it's the reason
that these tall ridges and hills exist
at Wolf Ridge today. Glaciers were so
powerful that we can still see marks of
them today, both in the landscape and on
individual rocks. This rock here has a
large glacial striations caused by the
glacier slowly dragging a rock against
this bedrock causing a large groove to
be ground into the stone. You may have
already guessed it, but this rock that
we're standing on here has to be pretty
tough in order to withstand all of the
scraping that the glaciers were doing on
this landscape. This rock here is called
anorthosite. The anorthosite is a less
dense form of rock than the other types
of bedrock found around it. So, when the
mid continental rift opened and the
magma started flowing out, this
anorthosite floated to the top kind of
like a marshmallow in hot cocoa. I think
we should rename it marshmallow mountain. Thanks for joining us this week for
geology. That was
fun! Yeah, that rocked. It was pretty gneiss
actually. Make sure you tune in next week
for our lesson on farming.
[Mumbles] Robby, I don't understand you [more mumbles] Robby you have to chew your food.
Have you ever met your farmer
and do you know where your food grows?
Join us next week for farming where we'll
learn a bit about the Wolf Ridge farm and
get to meet Sarah our farmer. I've got my
farming tools. Me too.
Whoa Robby I think I found one. Yeah, me too. Really? Look at mine. Oh! That's massive!
[laughter]
I don't really get why agates are so special. [pause] Because they're really tasty.
[music playing]
