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Earthquake If you are indoors when shaking starts: “DROP, COVER AND HOLD ON.” If you are not near a strong table or desk, drop to the floor against an interior wall and cover your head and neck with your arms. Avoid windows, hanging objects, mirrors, tall furniture, large appliances and cabinets filled with heavy objects. Do not try to run out of the structure during strong shaking.

If you are downtown, it is safer to remain inside a building after an earthquake unless there is a fire or gas leak. There are no open areas in downtown San Francisco far enough from glass or other falling debris to be considered safe refuge sites. Glass from high-rise buildings does not always fall straight down; it can catch a wind current and travel great distances. If you are in bed, stay there and cover your head with a pillow. Do not use elevators. If you use a wheelchair, lock the wheels and cover your head.

Changes in the Air Some volcanoes erupt quietly; others violently shoot gas, steam and ash into the air. After a volcano erupts, gases are released into the atmosphere. These gases include water vapor as well as carbon dioxide, sulfur dioxide, hydrogen sulfide, carbon monoxide, hydrogen gas and methane. All of these gases can form acid rain in high concentrations. Incorporated in the mass of gases expelled from a volcano exist tiny rock particles called tephra. Tephra particles can adhere to gas particles and be carried for great distances according to the U.S. Geological Survey. The immediate effect of high concentrations of gas in the air result in closure of the airspace above and around the volcano to air traffic. Over time, upper level winds can carry volcanic gases around the world.Ash particles impede air traffic as well as create immense breathing difficulties for people living near an erupting volcano. After a volcano, these 2-mm or smaller ash particles fly through the air, coating everything near the volcano. Ash particles can form a layer just like snow but it's much harder to remove. Combined with water, the ash becomes a mud-like mass. The Federal Aviation Administration monitors volcano eruptions to prevent planes from traveling in areas with possible ash particles in the air due to the dangers of loss of visibility and possible engine failure. Ash particle clouds also rise into the atmosphere for transportation with the prevailing winds, making their existence dangerous to any aircraft flying in the vicinity. Changes to the Landscape Every volcano makes a change to the landscape of the earth after an eruption. Volcanoes build new earth with every eruption, spewing hot lava from deep inside the earth onto the much cooler surface. After a volcano erupts, the magma flows down the sides of the volcano, reaching a point where it cools enough to stop flowing. As the flow progresses, everything in the lava's path is consumed. Plants, animals, buildings, roads, and trees are burned completely. Lava flows cool over time and form new rock. Wind, rain, and water after lava flows with weathering to break down lava and turn it into soil. When a volcano expels high volumes of ash, this coats the surface of the land around a volcano. This creates a dangerous condition of unstable earth with a thick layer of ash coating the sides of mountains and hillsides. Lahars are violent mudslides that result of waterlogged ash rushing down the sides of a mountain. These dangerous mudslides carry ash, rock, and debris, obliterating everything in its path. Changes to the Water Rivers and streams near erupting volcanoes suffer the effects of ash, hot gases and lava. After a volcano erupts, the debris expelled by the volcano affects waterways in a number of ways. Streams and rivers form a very basic part of the hydrologic cycle to disperse water through a drainage basin toward the sea. Volcanoes disrupt this process by blocking stream and river bed flows, re-routing courses, and contaminating the water supply with dangerous gases and particles. Fine ash can be carried away easily by water, but it takes time to restore a waterway after an eruption. Effects on Plants and Animals Like humans, animals can survive with little permanent effect resulting from ash deposition--as long as the ash isn't too hot and doesn't cover their source of food. The greatest threat from a volcano comes from damage to the environment. Ash quickly contaminates water, a necessity for any animal. Without access to an untainted water supply, many wild animals move to safer areas. Fish are extremely susceptible to a change in water quality. Volcanic eruptions often result in complete kills in streams and rivers near volcanoes. Ash contaminates the water, and burned or dead trees don't provide enough shade along these rivers to keep water temperatures down. High sediment content in the water prevents proper feeding, movement and reproduction. Birds naturally have difficulty flying in areas with ash clouds. Hot gases are deadly to birds as well. Plants and trees suffer from the effects of heat generated by the eruption and deposition of ash and sediments. However, unburned trees recover and usually continue growing after ash is washed off the tree itself. According to the U.S. Geological Survey, the increased amount of erosion possible with ash and tephra depositions creates slower re-vegetation of any damaged areas. Tephra contains potassium and phosphorus that are valuable nutrients for rich, fertile soil. Weathering helps release these nutrients into the soil, creating the prime environment for renewed growth of native plants and trees.

When two oceanic tectonic plates converge, one is subducted or pulled under, the other. This convergent activity allows for magma from the earth's core to erupt at the point of contact. The cooled erupted lava and debris build up over time. When the pile of debris and lava build up high enough, land is formed above sea level. This land is called an island. Often, these island volcanoes stay active, continuously growing.

The Ring of Fire, also known as the Circum-Pacific Belt, is a string of islands with active volcanoes in the Pacific Ocean. This geographical region is the most active volcanic and seismic zone in the world, and corresponds with oceanic-continental convergence of multiple tectonic plates.

Fasten all shelves securely to the walls. Use brackets to attach wall units, bookcases, and other tall furniture to wall studs. Standard steel brackets are fine and easy to apply. Place large, heavy objects on lower shelves or on the floor. They might fall during an earthquake and the less distance they have to fall, the better. You can also screw objects onto things, such as a desk.

Prepare disaster supplies in advance

Flashlight with extra batteries (preferably one for each individual) Portable, battery-operated radio with extra batteries Purchase and use "self powered radios" and "self powered flashlights". Batteries will be hard to find, if you can find them. Some models will charge cell phones, but the cell phone towers may be damaged, even destroyed. Purchase and use "glow sticks". These are safer than candles, since you will be dealing with ruptured gas lines, flammable, explosive gas. First aid kit and manual Emergency food and water (some sources say you should have up to 2 weeks worth of extra food on hand in case rescue workers cannot reach your location) Nonelectric can opener Essential medicines Cash and credit cards Sturdy shoes for each family member.

A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.

The short answer is that earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a rupture (break) surface.     Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motion of immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each other in some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other (like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the edges are distorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. An earthquake is the shaking that radiates out from the breaking rock.

Aftershocks, those who live through major earthquakes often say, are worse than the main shock in their own way. At least the main shock took them by surprise and was over fairly soon, in less than a minute usually. But with aftershocks, people are stressed already, dealing with disrupted lives and cities. They expect aftershocks at any minute, day or night. When a building is damaged by the main shock, aftershocks can take it down—maybe when you're inside cleaning it up.