As stated in section 1.1, physical geography is the spatial study of natural phenomena that make up the environment, such as rivers, mountains, landforms, weather, climate, soils, plants, and any other physical aspects of the earth’s surface.
This geography course isn’t going to focus too much on physical geography (you can learn more about that in earth science), but let’s cover some basic facts that will help us better understand the different areas of the world we’ll be covering!
What makes the seasons?
Seasons are the result of Earth’s orbit around the Sun and Earth’s axial tilt.
The definition of seasons is also cultural. In India from the ancient times, six seasons are based on south Asian religious or cultural calendars are recognized and identified even today for purposes such as agriculture and trade.
Ecologists often use a six-season model for temperate climate regions which are not tied to any fixed calendar dates: prevernal, vernal, estival, serotinal, autumnal, and hibernal.
Many tropical regions have two seasons: the rainy, wet, or monsoon season and the dry season.
Watch this video to see why we have seasons:
Did you know that when it’s winter in the northern hemisphere, it’s summer in the southern hemisphere? A student in Australia has summer break typically from mid-December to late January – just in time for Christmas! If you are a student in North America, your family may plan a summer camping trip sometime between July and August.
Why does the wind blow?
Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists of the bulk movement of air.
Wind is caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds.
Wind causes all sorts of natural phenomena such as tornadoes, dust devils, and waterspouts. Hurricanes and typhoons are tropical storms with winds from 72 miles per hour to 138 miles per hour. Powerful winds can cause terrible damage!
The earth’s surface is moving!
The movement of tectonic plates is another aspect of the earth’s dynamics that affects human activity. The earth’s crust, which is between 10 and 125 miles thick, is not one big solid chunk but rather a series of plates that cover a molten iron core at the center of the planet. The plates that cover the earth’s surface slowly shift and move. Plates can slide away from each other or they can collide, and they can slide parallel to each other in opposite directions. When two plates collide and one plate slides under an adjacent plate, the process is called subduction. Movement or shift where two plates meet can cause earthquakes and is usually associated with volcanic activity.
Mountain chains, such as the Himalayas, are a direct result of two plates colliding.
The collision pushes up the earth into a mountain chain, either by direct pressure or by volcanic activity. Plates can move up to an inch a year in active regions. Driven by the earth’s internal heat, these plates have created the planet’s mountain landscapes. Earthquakes and volcanic action along plate boundaries (called faults) continue to affect human activity and can cause serious economic damage to a community.
Where two tectonic plates meet is known as a plate boundary. Plate boundaries can be found near many natural edges of continents. Boundaries can interact in three different ways.
✦ Where two plates slide past one another is called a transform boundary. The San Andreas Fault in California is an example of a transform boundary.
✦ A divergent plate boundary is where two plates slide apart from one another. Africa’s Rift Valley was formed by this type of plate movement.
✦ Convergent plate boundaries occur when two plates slide towards one another. In this case, where two plates have roughly the same density, upward movement can occur, creating mountains. The Himalaya Mountains, for example, were formed from the Indian plate converging with the Eurasian plate.
In other cases, subduction occurs and one plate slides below the other. You can see an example of that in the picture above. Here, deep, under-ocean trenches can form. The 2004 Indian Ocean earthquake and tsunami occurred because of a subducting plate boundary off the west coast of Sumatra, Indonesia.
Watch this video to learn about plate tectonics. Note: There is a mention of millions of years.
Sometimes the activity of the earth’s crust causes earthquakes! An earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth’s lithosphere that creates seismic waves.
Watch this video about earthquakes by National Geographic:
Earthquakes can cause tsunamis. A tsunami (t)soo-NAH-mee, from the Japanese word: 津波, meaning ‘harbor wave’ is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake.
Earthquakes, volcanic eruptions and other underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami.
Unlike normal ocean waves, which are generated by wind, or tides, which are generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water.
Take a look at this TED-Ed video to see how tsunamis work:
Plate tectonics is associated with volcanoes. Watch this video to learn the science behind volcanoes:
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth’s crust, and then transports it to another location (not to be confused with weathering which involves no movement).
Erosion can be caused by natural things, but it can also be caused by people. Human activities have increased by 10-40 times the rate at which erosion is occurring globally. At well-known agriculture sites such as the Appalachian Mountains, intensive farming practices have caused erosion up to 100x the speed of the natural rate of erosion in the region. Erosion can decrease agricultural productivity due to the loss of nutrient-rich upper soil layers. In some cases, the eventual end result is desertification. You’ll study more about desertification in week 30 of Guest Hollow’s Geography & Cultures Curriculum.
✎ Seasons are caused by the earth’s axial tilt.
✎ Wind is caused by differences in the atmospheric pressure. Winds can cause damage.
✎ Plate tectonics can create mountains, cause earthquakes, and are associated with volcanic activity.
✎ A tsunami is generated by the displacement of water.
✎ Erosion is a powerful force that can be caused by natural means and/or by human activity.
Next: 1.4 Cultural Geography
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Image and additional text credits:
Wind article: https://en.wikipedia.org/wiki/Wind
By Map:USGSDescription:Muriel Gottrop~commonswiki – , Public Domain, https://commons.wikimedia.org/w/index.php?curid=35511
By NASA – http://www.nasa.gov/multimedia/imagegallery/image_feature_152.htmlOriginal unprocessed image: http://eol.jsc.nasa.gov/scripts/sseop/photo.pl?mission=ISS008&roll=E&frame=13304, Public Domain, https://commons.wikimedia.org/w/index.php?curid=63432
Haiti earthquake damage
By UN Photo/Logan Abassi United Nations Development Programme – originally posted to Flickr as Haiti Earthquake, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=8985699
By Jose F. Vigil. USGS – , Public Domain, https://commons.wikimedia.org/w/index.php?curid=478970