Climatic Factors In Soil Formation
Have you ever wondered why deserts have dry soil while forests have rich soil? The reason for this difference is climate. Of all the factors that influence soil formation, the climate is one of the most important. Climate is stable weather patterns over time. This includes conditions such as temperature and precipitation.
How does Climate Affect Soil Formation?
Climate is a direct influence on things such as soil moisture and temperature. These affect things like microbes in the soil, as well as the kind of vegetation that will grow. For example, the cacti that grow in Arizona won’t grow in the Amazon rainforest. Climate is important because it influences plants, which can transform soil. The roots of plants move around subsoil, distributing and absorbing minerals. When plants die they turn into humus and when humus decomposes it turns into topsoil. Basically, plants can take rock and turn it into fertile soil.
<Tree roots go the deepest compared to other plants. The roots expand small cracks, letting water and microbes go further down into the earth.>
Higher temperatures increase the temperature of the soil. The increase in temperature increases microbial activity. This means that microbes can break down humus faster. So places with warmer climates have thin layers of humus and very developed soil.
If temperatures are extremely high, all the water evaporates away. The dry soil makes it harder for plants to grow, so areas with high temperatures have fewer plants. Fewer plants means fewer animals, which both create humus when they die. So, the layer of humus is usually missing in places with high temperatures.
<A photo of a landscape so dry that the soil shrinks and cracks.>
Lower temperatures decrease the temperature of the soil. Lower temperatures also kill microbes, which can lead to very thick layers of humus. For example, leaves that fall in autumn can’t break down in the winter. This means that cooler climates don’t have a thick or nutrient-rich layer of topsoil.
In even colder regions, plants can’t grow at all. So, places with extremely cold climates often have less developed soil layers. In fact, cold climates have soil layers that are like deserts. This is because both regions don’t have plants to turn subsoil into developed topsoil.
<In arctic climates like this, the rock can’t develop into soil because it’s buried deep beneath the ice and snow. If you were to dig down, any soil you found would be pretty dry and rocky.>
How does Rainfall Affect Soil Formation?
Yet, it also contributes to chemical weathering. That’s because it dissolves the minerals in rocks. Geologists call this process leaching, and it is beneficial because the minerals help plants grow. More recently, polluting gases get dissolved into rainwater, turning rain into acid rain. In places with a lot of pollution, acid rain becomes a notable form of chemical weathering. This is because acid rain is strong enough to dissolve rock! In fact, it’s dissolving buildings and statues made out of marble and limestone.
We know that plants need water to grow, and the breakdown of humus puts nutrients back into the soil. But, too much rain can also lead to a build-up of humus. This is because the microbes that break down humus need oxygen to survive. When the microbes die, there is nothing to decompose the humus. Extensive rainfall also leaches a lot of nutrients out of the soil. It rains so much in tropical regions that the soil can’t absorb it fast enough. The flood water dissolves the minerals out of the soil and then contributes to nearby rivers and streams. This can be a problem for humans because the soil isn’t fertile enough to grow food.
<A photo of the Huay Mae Khamin waterfall in Thailand. The water is brown because flood waters containing dissolved minerals and sediment drain into the river.>
Arid climates receive little to no rainfall. These regions are prone to wind erosion. The dried out soil gets moved around by the wind, making it harder for plants to grow. With few plants to hold the dry topsoil down, the upper layers of soil blow away. If this happens often enough, the arid region can turn into a desert!