All About Water

Natural Disasters

Natural disasters are a natural hazards that causes human loss. Just a few natural disasters include hydrological disasters, earthquakes, and volcanic eruptions.

What Is a Natural Disaster?

A natural disaster is a natural hazard, but a natural hazard is not necessarily a natural disaster. A natural disaster becomes a natural hazard when it occurs near vulnerable human populations. Natural disasters kill people and cause financial damage. For example, an earthquake that strikes an uninhabited place is a natural hazard, but not a natural disaster because it doesn’t kill people or destroy human property. An earthquake that strikes San Francisco, however, is a natural disaster. The amount of damage that a natural disaster creates depends on people’s resilience, their ability to withstand and resist the disaster. Natural disasters come in a variety of forms.

Hydrological Disasters

Hydrological disasters are natural disasters caused by water. Hydrological disasters include floods, tropical cyclones, and tsunamis. Floods are often created by tropical cyclones, which produce storm surge. Tsunamis are caused by underwater earthquakes. Japan’s 2011 Tohoku earthquake and accompanying tsunami is estimated to have killed up to 25,000 people.

Earthquakes

An earthquake is a shaking of the Earth’s crust that happens when tectonic plates collide. These shakings differ in magnitude depending on the force of the tectonic plates’ collision. The underground place where the tectonic plates collide is called the “focus.” The point directly above the focus, which suffers the most damage, is called the “epicenter.” An earthquake alone won’t usually kill people or wildlife. However, earthquakes usually trigger secondary events that do cause damage. Earthquakes make buildings collapse and cause fires and tsunamis. These secondary events are what cause earthquakes to be perceived as natural disasters.  Societies can lessen their vulnerability to earthquakes by monitoring underground activity, warning people when earthquakes are going to occur, planning evacuations, and by building safer buildings and safety systems.

Volcanic Eruptions

Volcanic eruptions can destroy their surroundings in several ways. The initial volcanic explosion can produce dangerous rock falls. The lava produced by volcanic eruptions may trickle down, destroying nearby buildings and plants. Volcanic eruptions also produce toxic ash clouds, which can settle over nearby places. Even the smallest quantities of ash are toxic if inhaled, and enough ash can collapse roofs. The most destructive part of a volcanic eruption is pyroclastic flows, collections of hot volcanic ash clouds that rush down slopes. Historians believe that pyroclastic flows destroyed Pompeii. Volcanic eruptions, however, are some of the most visually astounding kinds of natural disasters.

The xylem and phloem are the two kinds of tissues that transport water and other nutrients within plants. The xylem carries water up through the plant. The phloem transports nutrients, most notably glucose, down throughout the plant.

Xylem and Phloem: The Xylem

In Classical Greek, “xylem” translates to “wood.” This makes sense, as the most common xylem tissue is wood. The xylem supply all of the parts of a plant with water by transporting water up through the plant. Xylem are long tubes called vessels. They pump water from the roots up, replacing the water that plants lose to transpiration and photosynthesis.

Xylem and Phloem: How the Xylem Transport Water

Plants depend on xylem to replace the water that evaporates off of their leaves. The xylem can transport their sap through transpirational pull. In transpirational pull, water transpires, or evaporates, off of plant surfaces into the atmosphere. As transpiration pulls water out of the plant, the water tension within the plant pulls water from the plant’s roots and soil back into the leaves. This water tension is strong enough to lift water hundreds of meters above the ground into the highest branches of trees. However, for transpirational pull to work, the xylem vessels must be very compact in diameter, as this compactness maximizes pressure.

Xylem and Phloem: Other Ways That the Xylem Transport Water

The xylem can also pull water and nutrients up through the plant via root pressure. Through osmosis, plants absorb water into their roots. This osmosis then forces sap up the xylem and into the leaves. The xylem are also aided by capillary action, the force by which water adheres to the surface of xylem pipes. This capillary action balances gravity.

Xylem and Phloem: How the Phloem Work

Phloem is the second transporting tissue in vascular plants. The phloem carry nutrients, most notably glucose, down throughout the plant. Like “xylem,” “phloem” derives from Ancient Greek. “Phloem” translates to “bar,” which makes sense, as phloem is the innermost layer of bark in trees. Phloem transport the nutrients that plants produce in photosynthesis. The phloem’s transportation is called translocation. Translocation moves the phloem’s sugar-rich sap from sugar sources to sugar sinks. Plants generally store their sugars in their roots, and the phloem transports sugar from the roots to the growing areas in the plant, the sugar sink.

Differences Between the Xylem and Phloem

The xylem and phloem both transport vital commodities through plants. However, the xylem and phloem differ in several ways. While the xylem transport mostly water, the phloem transport nutrients, especially glucose. The xylem are made up of dead cells, while the phloem are made up of living cells. Xylem only transport sap upward, while the phloem are multidirectional—they move sugars wherever they’re needed. To work, the xylem rely on water tension, while the phloem rely on translocation.

The Science and Story of Rainbows 

Rainbows fascinate us. We find them in nature, and then expound upon and replicate them in our religions, mythologies, literature, art, and music. In this article we will talk about the science of rainbows, our cultural perception of rainbows, and we will learn how to make a rainbow.

How to Make a Rainbow: What Is A Rainbow?

The bright rainbows that we see in the sky are “primary rainbows,” which are red on the outside of their arcs and violet on the inside. They are caused by the light that is reflected from water droplets. Although we artificially subdivide rainbows into “bands,” the colors present in rainbows are not actually separate from each other. A rainbow is a continuous spectrum of colors. Infamous “double rainbows” appear as a color-inverted second arc above a primary rainbow. Rumored “triple rainbows” are scientifically impossible and cannot naturally occur.

How to Make a Rainbow: Where Do We Find Rainbows?

We can find rainbows wherever we find sunlight shining through airborne water droplets at a low angle. We can find rainbows around rainclouds, waterfalls, and fountains. We perceive rainbows to be brightest when half of the sky is still dark with rainclouds. Sometimes, when the moon is bright enough, we can even find moonbows, or nighttime rainbows. Interestingly, one cannot actually be “under” or “at the end of” a rainbow: even if you are looking at someone who appears to be at the end of a rainbow, from their vantage point, the person sees the rainbow as being still further off yet. This means that rainbows are not actual, physical objects that we can physically approach. So much for pots of gold.

How to Make a Rainbow: Rainbows in Science