Geography

Geography is the study of the physical features of the Earth and its atmosphere. This page outlines the world building aspects of Turubai's physical features. This is a very broad page that covers a variety of disciplines and topics.

## Tectonic Plates

    Tectonic plates are massive pieces of the planet's crust that naturally move over time. This alters the features of the planet's surface. In order to create a realistic geography, it is important to follow the consistent rules of tectonic plate theory.

### Types of Boundaries

Three plate boundaries exist, and each boundary is associated with different features on the planet's surface.

1. Divergent: Plates side apart from each other.
	* Ocean/Ocean: Form by seafloor spreading. A mid-ocean ridge is created, causing small volcanoes and shallow earthquakes.
	* Continent/Continent: Land splits, possibly creating a new ocean basin. See the East-African Rift Valley.
2. Convergent: Two plates slide toward each other.
	* Subduction: One plate moves under the other.
		+ Ocean/Continent: The dense oceanic lithosphere plunges beneath the less dense continent. A trench usually forms, and volcanoes are common. Mountains are created on the continent. See: The Andes
		+ Ocean/Ocean: Denser (older, cooler) crust slips under the lighter crust. This creates earthquakes and a deep trench. See: The Mariana Trench
		+ Continent/Continent: Neither mass is subducted, so the plate edges are compressed and uplifted. This creates a massive mountain chain. See: The Himalayas
3. Transform: Two plates slide (or grind) alongside of each other. Strong earthquakes are created along the fault. See: California

## Prevailing Winds

The prevailing wind in a region on the planet's surface is a surface wind that blows predominantly in one direction. These are the result of global patterns in movement in the atmosphere. In general, winds are easterly at low latitudes and westerly in mid-latitudes.

    Sand dunes can orient themselves perpendicular to the prevailing wind direction in coastal and desert locations. Insects drift along the prevailing wind. Prevailing winds in mountain lcations can lead to significant rainfall gradients.

### Mountains

    A rain shadow is a dry area on the leeward side of a mountainous area. The mountains block the passage of rain-producing weather systems and cast a  shadow of dryness behind them. Wind and moist air is drawn by the prevailing winds towards the top of the mountains, where it condenses and precipitates before it crosses the top. The air advances across the mountains, creating a drier side.

Western North America, such as the Great Basin encompassing states like Nevada, are the results of the rain shadow of the Rocky Mountains.

## Water

Hydrology is the study of the movement and distribution of water. Water plays a core role in every system on the planet, both human and natural.

### Groundwater

Groundwater is water beneath the surface of the planet. Humans often pump water out of the planet for drinking. An aquifer is an underground layer of water-bearing permeable rock. In other words, the rock is porous and can hold the water similar to a sponge. Most land areas on Earth have some form of aquifer underlying them, sometimes at significant depths. They are critically important in human habitation and agriculture. See the Ogallala Aquifer in the Central United States for an example of a major aquifer.

### Water Cycle

This process describes the continuous movement of water about the surface and atmosphere of the planet. Condensed water vapor falls to the planet's surface in the form of precipitation (rain, fog, snow, hail, etc.). Runoff includes the variety of ways which water moves across the land. Evaporation can occur at any point in the process; this is the transformation of liquid water back into a gas. The gaseous water then condenses back to liquid in the atmosphere.

Natural arch produced by wind erosion in Jordan.Horseshoe Bend, an incised meander of the Colorado River.Eroding rill in a field used for farming.A sea cliff produced by coastal erosion in China.A rock formation in Bolivia sculpted by wind erosion.Glacial moraines in Canada.
An important result of this process is erosion, the movement of material (like soil) across the crust. This is caused by water, ice, snow, and wind. This radically alters the properties of land over time, creating natural forms found everywhere.

### Drainage Basins

A drainage divide is elevated terrain that separates neighboring drainage basins. The divide lies along topographical ridges in the form of a range of mountains or hills. This is known as a dividing range. Any precipitation that falls within one drainage basin will always flow out to a specific body of water. Sometimes, much of the water will converge into one river such as the Mississippi River.

An endorheic basin is a limited drainage basin that retains water and allows no outflow to other bodies of water. An example of this is the Great Basin in the Western United States. Endorheic water bodies include some of the largest lakes in the world. These regions can occur in any climate, but are most commonly found in desert locations. In areas with higher rainfall, riparian erosion will generally carve drainage channels, or cause the water level to rise enough that it eventually finds an outlet. Examples of relatively humid regions in endorheic basins often exist at high elevation. These regions are usually marshy and are subject to substantial flooding. An example of this is the area containing Mexico City.

### Ocean Currents

On Earth, ocean currents flow clockwise in the northern hemisphere and counterclockwise in the southern hemisphere in circular patterns that tend to trace the coastlines. Warm water from the equator gets transported to the poles and cold water from the poles to the equator. Due to the moderating effects of the ocean currents, Earth's seasons actually lag behind the actual position of the Earth's tilt relative to the sun.

Ocean waves mixing with wind and currents can help store heat deeper in the ocean. This further stabilizes Earth's climate. Ocean currents thus have a huge impact on the climate in particular regions. Europe is surprisingly far north given its climate; this is thanks to the ocean current patterns in the Atlantic. Rome is at the same latitude as New York.

Surface ocean currents are largely wind driven and can result in both horizontal and vertical movement. Horizontal surface currents that are local and typically short term include rip currents, longshore currents, and tidal currents. In upwelling currents, vertical water movement and mixing brings cold, nutrient-rich water toward the surface while pushing warmer and less dense water downward. This creates a cycle of upwelling and downwelling.

Depp ocean currents are density driven and differ from surface currents in scale, speed, and energy. Water density is affected by the temperature, salinity, and depth of the water. The colder and saltier the water is, the denser it is. The greater the density differences between layers of water, the greater the mixing and circulation.

### Rivers

Because of how water collects via rain shadows, rivers tend to begin forming in mountains or hills. Rain water or snowmelt collects and forms small streams that grow in size as you move down stream. Rivers eventually flow into larger bodies of water, like lakes or oceans. In drier areas, rivers may evaporate before reaching a body of water.

Rivers naturally flow to the lowest point between mountains or hills. Their power is dervied from gravity. They can follow a complex and meandering path, and do not necessarily take the shortest path. The type of terrain that the river flows through impacts the meander of the river.

Due to erosion, rivers can deepen valleys and move rocks.

## Other Geographical Features

### Coasts

Land is more variable in temperature than water. It heats up faster than the ocean during the day, and cools faster at night. Areas on the coasts are thus more moderate in temperature compared to areas farther inland. For similar reasons, humid air also acts as a moderator for an area's temperature.