the Alps leading thousands of soldiers, horses,  and the infamous elephants to victory over Rome.  

It was a tremendous undertaking, and knowing  the lay of the land or gaining strategic  

control of mountain passes and rivers  has often been key to empire building.

But we'll leave the plot of  that story for world history.  

Today we'll focus instead on the setting:  the landscapes over which they travelled.

The topography, or shape of a region or land, has  influenced so much -- like lifestyles, economic  

activities, and transportation. We've even  gotten different cultures and languages thanks  

to isolated communities flourishing in places  that are hard to access by the outside world.

So as physical geographers, we want to know how  the scene -- the Earth -- was set. Like what  

shaped the surface of the Earth and led to so  many different landforms, or features. And have  

they always existed, or has the land changed over  time? And why is that volcano here and not there? 

We already know the Earth is the result of many  processes -- and its topography is no different.

Some processes operate deep within the Earth's  interior and some stay at the surface. But just as  

the atmosphere and biosphere are always changing  with the flow of energy and cycle of nutrients,  

these processes in the lithosphere  change the very ground beneath our feet.

I'm Alizé Carrère, and this  is Crash Course Geography.

INTRO

Whether we live in a city, a suburb, or the  countryside, we're embedded in particular  

landscapes. We see these hills or ponds or  lakes every day, and they become ordinary to us.

So we visit impressive landscapes,  like the places we now call Half Dome  

in Yosemite National Park in the US, Uluru  in Australia, or the Serengeti Plains in  

Tanzania -- all natural environments that  fill us with a sense of grandeur and awe.

But no matter where we are, the land  is made up of physical features,  

like hills, valleys, and plateaus. And we can study all these physical  

features -- even the ordinary ones. Geomorphology  is the scientific study of landforms,  

the processes that make them, why they vary,  and their significance at different scales.

Towering mountains or flat plains  that stretch as far as the eye can see  

can seem timeless, but they're  actually always changing thanks  

to a network of intertwined systems  that recycle and re-shape the Earth.

Like the rock cycle moves  minerals through igneous,  

sedimentary, and metamorphic phases  that shape much of the Earth's crust,  

and relies on processes both deep  inside and on the surface of the Earth.

And where those rock cycle processes  are forming and destroying rocks  

follows a pattern we call the tectonic cycle.  The tectonic cycle works on a huge scale and  

moves vast sections of Earth's crust called  plates around the globe, which creates major  

geographic features like mountain ranges,  ocean basins, and continental shields.

And there's the hydrological cycle which  explains how water is continually transferred  

between being liquid, gas, or solid as it  circulates into and out of the atmosphere,  

lithosphere, hydrosphere, and biosphere -- each of  which is its own system with numerous sub-systems.

The rock, tectonic, and hydrological  cycles and their many subsystems  

make up the geological cycle. They also  showcase the give and take between two  

overarching internal and external systems  that shape the topography where earth,  

atmosphere, and ocean all come together:  endogenic and exogenic processes.

Endogenic processes are forces that  originate from within the Earth.  

Like igneous processes which eject fresh  rock from the interior onto the surface  

and tectonic processes which  work to raise or lower the land.

They produce initial landforms like continental  landmasses, ocean basins, and mountain ranges  

that span entire continents. So it's kind of like  making the initial broad strokes in a painting.

Like continental landmasses, ocean basins, mountain ranges that span across entire continents.

The fine details will come later.

To create landforms from  igneous and tectonic activity,  

the rock cycle, the tectonic cycle, and  the hydrological cycle trigger each other  

above and below ground in a variety  of ways that change the topography.

The powerful forces unleashed by tectonic  activity as plates shift around the globe  

and cause earthquakes and tsunamis put  rocks under tremendous stress. And rocks  

respond to stress differently  depending on whether they're on  

the surface or buried deep down. Rocks at the surface are brittle,  

and when tensional forces from moving plates  pull the crust in different directions,  

they come under stress or pressure and break  or fracture in a process called faulting.

These cracks or faults in the Earth's crust  show how the rock has moved on either side.  

The rock might've moved horizontally or vertically  as little as a centimeter or up to 15 meters over  

years, decades, or even centuries. Like  in September 2005 a series of earthquakes  

occurred along a segment of what's called the Afar  Depression, creating an opening eight meters wide.

Though this was nothing new for the  region, because the Afar Depression  

is an area of open fissures and faults at  the northern tip of the Great Rift Valley.  

And the Great Rift Valley is a primary  branch of the East African Rift System,  

which extends from present-day Jordan  in the north, through the Dead Sea and  

the Red Sea and along the length of East  Africa to the mouth of the Zambezi River.

Kind of like how the volcanoes of the Ring of Fire  mark the plate boundaries of the Pacific Ocean,  

the East Africa Rift system lies along the  boundaries of three tectonic plates – the Arabian,  

African-Nubian and the African-Somalian  plates. It's a huge set of faults that  

started to form when the plates began  to diverge about 25 million years ago.

The sudden rift in 2005 was just a small  step in the long process currently tearing  

the northeast of Ethiopia and Eritrea  from the rest of Africa. Eventually,  

it will create a new ocean -- but  that will take millions of years.

In particular, some of the faults of the  East African Rift system are normal faults,  

a common type of fault created where  the crust is moving apart vertically.  

On a grand scale, when pairs of  faults work together, they produce  

block or fault-block mountain  ranges like the Vosges in France.

Though faults and fissures -- and  the volcanic and earthquake activity  

that comes along with them -- haven't  prevented humans from living on the edge.

Tectonic clashes in the Great Rift Valley  have carried on for tens of millions of years.  

But just a few million years ago  the journey of human evolution was  

recorded in the sediments and fossils  throughout the region that some call  

the “cradle of humanity,” as our early pre-human  ancestors walked and climbed across these valleys.

Today, the fertile slopes of the many volcanoes  that dot the length of the rift and the deep  

elongated lakes on the valley floor are  home not only to wildebeest, giraffes,  

zebras, impalas, and elephants, but  also to some of Africa's biggest cities.  

They're also important agricultural production  zones exporting coffee, tea, and sisal.

But faulting isn't the only way the tectonic  and rock cycles combine to create landforms.  

Unlike brittle surface rocks that break when  stretched or extended, deeply buried rocks  

that are heated and compressed over a long  period can bend in a process called folding.

Remember, sedimentary rock forms horizontal  layers or strata. And when they're squeezed or  

compressed -- like when two continental plates  collide at converging plate boundaries -- they  

bend into arches called anticlines which  are separated by troughs called synclines.

It's like if we lay out a piece of thick  fabric and then suddenly bunch it together  

from both ends to get folds. Doing that  with Earth's surface gives us fold belts,  

like the Jura Mountains of France and Switzerland.

Both folding and faulting produce large  scale landforms and shape the landscape  

in really dramatic ways. Like both can  be part of the mountain building process  

called orogenesis, which literally  means “the birth of mountains.”

And really, orogenesis is just more ways the  rock cycle interacts with the tectonic cycle.  

Mountains are just rock masses that  have been elevated high above their  

surroundings by tectonic processes  along plate margins as plates move.

Like when the Indian plate buckled into  the Eurasian plate, vast folded and faulted  

mountain belts rose, and rocks in the crust  were thickened, deformed, and metamorphosed.  

The collision created the Himalayas, which  are really more like three broadly parallel  

ranges that each mark a different  sequence in the uplift process.

Processes that are still happening.  Currently the Indian plate pushes  

northward at the breakneck speed of 5 cm a year,  

causing the Himalaya Mountains to continue to  grow at the rate of one centimeter each year,  

or 10 kilometers every million years. Which  in geological terms, is like warp speed.

Mountain ranges can also grow from other  endogenic processes like volcanism,  

which is when lots and lots of volcanic rock  builds up as magma is pushed out on the surface.

Like on the Kamchatka Peninsula  in the Russian Far East,  

which is a dramatic volcanic  landscape of immense beauty.  

On this relatively small bit of coastal land there  are over 300 volcanoes, of which 29 are active.

The volcanoes are mountains or hills  constructed from igneous processes  

when magma deep within the Earth erupts onto the  surface as lava, and then cools and solidifies.  

Most commonly, magma reaches the surface where  two plates meet, which is why many volcanoes  

are located above subduction zones where one  tectonic plate is being dragged under another.

Here in Russia, the Kamchatka Peninsula lies  to the west of the Kuril-Kamchatka trench,  

where the plunging Pacific plate creates a  subduction zone and causes volcanic activity.

So when we're looking at an  active volcano or any mountain,  

what we're really seeing is part of Earth's  tectonic cycle unleashed through endogenic  

processes which bring fresh rock to the  surface and move and deform the crust.

So our picture of the Earth is coming along  nicely. Once the land has been dramatically  

lifted or torn apart by tectonic forces  and the internal rumblings of the Earth,  

initial landforms like mountain masses  are sculpted into sequential landforms.

These are the details -- the  [happy little] peaks, valleys,  

and other features honed by external or  exogenic processes acting on the surface  

that remove rock materials and reduce the land. In endogenic processes, the tectonic and rock  

cycles are the main players shaping the  Earth's crust, but in exogenic processes,  

the hydrological cycle comes into its  own as it interacts with the rock cycle.

Water circulating from the ocean to the atmosphere  is important in the annual march of seasons, but  

also in the geological cycle by which  Earth renews and reproduces itself.

Like the vapor in the atmosphere  comes down to produce life and growth  

and create soil from rock through weathering or  the decay and disintegration of rocks. Over time  

the weathered rock is picked up and carried by  water, wind, and ice in the process of erosion  

where it accumulates to make sedimentary rocks  or gets subducted with the diving oceanic plate.

Different rocks offer different resistance  to weathering and erosion based on everything  

from grain size and hardness to porosity and  permeability to their mineral composition.

But resistance actually has a big influence  on how landforms and landscapes look.  

Rocks that are resistant to weathering and erosion  will stand higher than less resistant rocks.  

And weathered rock is more easily picked  up, moved, and deposited somewhere else.

Like when folds are deeply eroded like in the  Appalachian Mountains along the eastern part  

of the US, they end up as ridges and valleys.  As weaker rock like shale and limestone eroded,  

it left hard sandstone and quartzite to  stand as long narrow parallel ridges.

And the ridges have been cut through  and further eroded by rivers.  

These breaks influenced migration, settlement  patterns, and even cultural traits in the US  

in the 1700s as the flow of people, goods,  and ideas were guided by this topography.

Weathering and erosion have also left  behind some of our most stunning landscapes.  

Like in the remote, dry interior of  Australia's Outback stands Uluru,  

a sandstone formation called an inselberg  that we think is 550 million years old.

It looks like a 348 meter tall rock that's 9.4  kilometers around was just dropped onto the land.  

But Uluru is an erosional remnant and  all that remains from an ancient plain  

that would've been level with the present dome.

Centuries of erosion by wind and water have  removed the weaker rock and left erosion-resistant  

rock domes like this one standing above the  surrounding landscape. Uluru is the most famous  

and is sacred to the traditional landholders who  have lived around the rock for thousands of years.

Cliffs and canyons, beaches and  dunes, floodplains and river valleys,  

plateaus and mountains -- these are all  products of a restless Earth and greatly  

influence how people live and derive meaning  and a sense of place in different landscapes.  

Ultimately landscapes are part of our collective  human experience, our struggles, and our triumphs.

In the next few episodes we'll talk more about  endogenic and exogenic processes -- especially  

weathering, erosion, and the power of  water -- because of how fundamental  

they are to both the ordinary and  extraordinary landscapes around us.

The Earth does change beneath our feet. Sometimes  infinitely slowly as with tectonic processes and  

sometimes instantly when volcanoes erupt. Next  time we will look at the grand fireworks show  

that nature puts up to see the different types of  volcanoes and different landscapes they produce.

Many maps and borders represent modern  geopolitical divisions that have often  

been decided without the consultation, permission,  or recognition of the land's original inhabitants.

Many geographical place names also don't reflect  the Indigenous or Aboriginal peoples languages.  

So we at Crash Course want to acknowledge these  peoples' traditional and ongoing relationship  

with that land and all the physical  and human geographical elements of it.

We encourage you to learn about  the history of the place you call  

home through resources like native-land.ca  and by engaging with your local Indigenous  

and Aboriginal nations through the  websites and resources they provide.

Thanks for watching this episode of Crash  Course Geography which is filmed at the Team