Transcript Weathering
19 Extreme Environments Hot Deserts Why are Deserts Cold During the Night? 20 Extreme Environments Hot Deserts What are hot deserts like? Climate You may be asked to describe what these graphs show. Refer to: Highest, Lowest, trends, anomalies. Include Data, months, increases/decreases seasons, links between Rain/Temp 21 Extreme Environments Hot Deserts What are Hot Deserts like? Vegetation For vegetation to survive in desert they must adapt. Challenges: Extreme heat, lack of water/nutrients 1) Xerophytes These plants have made physical adaption's to survive the desert e.g. Cacti. Some of the features are: - Spines – These deter predators and help to break up wind – reducing the amount of transpiration of water moisture -Shallow roots – these quickly draw up any surface rainwater. -Deep roots – Reach towards deep underground water stores. -‘pleated’ body – The cactus can swell up to take in water -Green body – body takes on role of photosynthesis. -Small surface area – to reduce transpiration -Thick waxy body – the make sure no water is lost 22 Extreme Environments Hot Deserts What are Hot Deserts like? Vegetation For any vegetation to survive in a desert it must adapt. The main challenge is the heat & lack of water 2a) Ephemerals (plants) These plants lie dormant for months, or even years in the desert until it rains. These plants grow & flower very quickly (within a few days) before the water gets evaporated or soaked away. 2b) Ephemerals (seeds) In deserts there are many seeds waiting to be germinated. When the rains come they will quickly start to grow into plants, taking advantage of the conditions 23 Extreme Environments Hot Deserts Xerophytes A sketch to show key features of a cactus What are Hot Deserts like? Vegetation Ephemerals Desert after a ‘rain’ event 24 Extreme Environments Hot Deserts What are hot deserts like? Animals Animals need to adapt in order to survive in desert environments. They have to cope with extreme temperatures, lack of food and lack of water. To avoid daytime heat, many desert animals are Nocturnal; they burrow beneath the surface or hide in the shade during the day, emerging at night to eat. Many desert animals do not have to drink at all – they get all of their water from the moisture in food 25 Extreme Environments Hot Deserts What are hot deserts like? Animals How have camels adapted to life in deserts? Thick fur & underwool – warmth at night & insulation against sun in day Fat Stored in humps - energy reserve Concentrated urine to retain as much water as possible Broad, flat leathery pads on hooves to spread out weight on sand Two rows of eyelashes– protects against sand & sun Nostrils can be closed to keep out sand Thick leathery patches on knees to protect when resting on hot sand Long, strong legs – carry heavy loads & body further away from sand 26 Extreme Environments Hot Deserts What are hot deserts like? Weathering & Erosion What is weathering? Weathering is the action of the weather, plants and animals on rocks. The rocks are broken down without being removed. What is Erosion? Erosion is the wearing away and removal of rock, soil etc by rivers, sea , ice and wind. 27 Extreme Environments Hot Deserts What are hot deserts like? Weathering & Erosion Different Types of weathering: a) Biological Weathering - The growing roots of plants in a crack within a rock can force the rock apart. b) Physical /Mechanical Weathering A B The action of the weather through repeated heating/cooling or freezing/ thawing of water on rocks. E.g. Freeze thaw/ frost Shattering (picture A) or onion skin weathering/Exfoliation (picture B) c) Chemical Weathering – Rainwater that is slightly acidic can dissolve rocks. This is most clearly seen on statues 28 Extreme Environments Hot Deserts What are hot deserts like? Weathering & Erosion In hot Deserts Physical Weathering occurs in the form of ‘Freeze thaw’ and/or ‘Onion Skin Weathering’ Water enters a crack on in the rock. When its cold (at night) the water freezes and expands. The water then thaws. This process is repeated. Eventually pieces break off When rocks are made up of different layers, they can be made of slightly different materials. These materials respond differently when repeatedly heated /cooled. The rocks expands &contracts at different rates. The outer layers then break off. Freeze-Thaw Weathering Exfoliation / onion skin weathering 29 Extreme Environments Hot Deserts What are hot deserts like? Weathering & Erosion b) Chemical Weathering. This includes Salt Crystallisation (water evaporates & leaves behind salt, which expands) and Hydration (water reacts with chemical in the rock) c) Biological Weathering. This is when plant roots grow into crack in the rock and force the cracks open. Erosion is the wearing away and removal of material. In deserts erosion is mainly caused by the wind. Although flash flooding can also happen & moves lose material. Both occur as there is little vegetation hold /bind sand. Deposition is the laying down of material that has already been eroded. Material from wind erosion often deposits is often laid down to form Dunes & flash floods carry material further down the valley & across flood plains 30 Extreme Environments Hot Deserts Formation of Zeugen Stage 1 When there are alternating layers of hard & soft rock there can sometimes be weaknesses in the joints. When the temperature changes and dew occurs at night, chemical weathering breaks up the rock and starts to open up the joints What are hot deserts like? Physical features – Zeugen 1 31 Extreme Environments Hot Deserts Formation of Zeugen Stage 2 Once the joints are opened up, they are then eroded away further by the wind (abrasion). This forms ridges and hollows. At this stage the erosion starts to reach into the soft rock What are hot deserts like? Physical features – Zeugen 2 32 Extreme Environments Hot Deserts Formation of Zeugen Stage 3 The Zeugen can stand between 3m – 36m high. Now that abrasion starts to erode the softer rock (which is less resistant), rock pedestals will often form What are hot deserts like? Physical features – Zeugen 3 33 Extreme Environments Hot Deserts What are hot deserts like? Physical Features Rock Pedestal Rock Pedestal–These are sometimes called mushroom rocks as they are often ‘top heavy’. Over time, the wind (which carries particles of sand) wears away the rock. This type of erosion is called abrasion. A rock pedestal erodes more in places than others. This is because softer (less Example of a Rock Pedestal Classic mushroom resistant) rock shape at he top erodes more quickly More resistant rock than harder (more worn away slowly resistant) rock and because much of Less resistant rock worn away quickly the erosion takes Most erosion within place within the first first metre of ground metre of the ground as wind lifts material 33 Extreme Environments Hot Deserts What are hot deserts like? Physical Features Rock Pedestal You need to be able to draw and label a rock pedestal from memory 34 Extreme Environments Hot Deserts What are hot deserts like? Physical features – Yardang Key Yardang: Formation Yardangs often form in alternate vertical bands of hard and soft rocks. The weaker rocks are less resistant to the wind Stage 1 – flat surface Cross section view erosion & erode more quickly. The harder rocks are more resistant and Stage 2–Differential erosion due to abrasion left as ridges. Hard, Resistant Rock Softer, less resistant rock 35 Extreme Environments Hot Deserts What are hot deserts like? Physical features – Yardang Yardang: Formation Stage 3 – Ridges become more pronounced Yardangs are long and thin in appearance. The ridges become more pronounced. Can be up Cross section view to 15m high They also often occur parallel to the prevailing (most common) wind direction, this is when most erosion will occur. Diagram is plan view What are hot deserts Extreme like? Physical features/transportation Environments – Wind transportation Wind can Transport sand in a variety of ways. The stronger the wind, the more material can be transported. 1) Suspension-Light/finer material is carried/suspended in the air 2) Saltation – Suspension This material is ‘bounced’ along the ground Saltation 3) Traction – Traction This material is heavier and is blown/rolled along the ground 36 Hot Deserts 37 Extreme Environments Hot Deserts What are hot deserts like? Physical features/transportation – Wadi A Wadi is a steep sided, deep, flat floored (dry) valley in a desert. Usually they do not have any water in them. There may be a few desert plants in the Wadi. The material in the wadi is often loose. Therefore, when there is a flash flood, lots of material in the wadi is transported (moved) & then deposited (dropped) further down the valley. Steep Sides Loose Material Flat bottom Some plants