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Year 7 & 8 TOC

Water in nature

Nature & the water cycle

LO:Investigating factors that influence the water cycle in nature

Water has been cycling around the earth since it was first formed and while the amount of water hasn’t changed, how the water cycles is influenced by many factors, like temperature and wind. 

A great example of the water cycle changing in nature is the El Nino and La Nina effects. A lot of what happens in the air is because of the temperature of the water. 

Remember, temperature increases the speed at which molecules move. The hotter the water is the more water vapour rises. 

More than half the time, we are in a neutral phase. In this phase, the sun warms the water near the equator creating clouds. Trade winds then blow from east to west, causing water water in the west (towards Australia) and cooler waters in the east (close to South America). 

El NiÑo

El Niño is an abnormal weather pattern, caused by extreme warming of the central and eastern Pacific Ocean. During El Niño, the tradewinds weaken or even reverse. This warm water displaces the cool water that normally sits in the east close to South America. While this may not sound like a big thing, it actually has a major effect on many different parts of the world including Australia. 

For Australia this means less rain fall, more heat waves and fewer tropical cyclones for eastern and northern areas.

There’s nothing special about this event, in fact it’s been happening for thousands of years and occurs roughly 4 – 7 year, lasting for 12 -18 months. What is special, is the ocean temperature, wind pattern and rain fall of each El Niño event. 

La NiÑa

La Nina events are the opposite of El Niño events. Unlike El Niño, where the trade winds aren’t strong or revered, the trade winds are much stronger. They end up causing more rainfall and even widespread flooding. You can particularly see this in parts of Queensland and Victoria. 

Nine of the ten driest winter/spring periods on record for eastern Australia occurred during El Niño years. The Murray–Darling Basin, rainfall average catchment was 28% lower during El Niño years. The droughts of 1982, 1994, 2002 and 2006 are all associated with El Niño.

During La Nina, the opposite happened. The average catchment was 22% higher and caused severe floods in 1955, 1988, 1998 and 2010. The below image is of the 2010 Queensland floods. 

Volcanic eruptions

In 79 AD Mt Vesuvius erupted, spewing ash hundreds of feet into their air for 18 hrs! Ash and toxic fumes poured out on the town of Pompeii, filling up courtyards, collapsing roofs and blocking doors.  

The images below show Mt Vesuvius and the people who lived in Pompeii at the time of the eruption. When the volcano erupted, it was so quick that many people died of burning, suffocation or being crushed by debris. Ash fell on the town and people so quickly that many of them became encased in this. When archaeologists re-discovered Pompeii, they also discovered bones in side air pockets. Soon they poured plaster into the air pockets, revealing people’s positions during the eruption. 

As with Vesuvius, when volcanos erupt they release large amounts of dust and particles into the air. As these particles float in the air, they reflect light and prevent the earth from being heated. This includes water and, as a result less evaporation. This leads to less rain. Constant/frequent volcanic action can leas to areas becoming drier.  

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