Earthquakes, Volcanoes and Severe Weather Natural Hazards Earthquakes, Volcanoes and Severe Weather

What is an earthquake? When the stress built up between two blocks of crust over comes friction, an earthquake occurs While stress is being “built up,” this is stored elastic energy When the earthquake occurs, the elastic energy is converted into mechanical energy Focus Epicenter Seismic Waves

Seismic Waves P waves S waves Surface waves Primary waves First to arrive, move fastest Compression waves Feels like a punch or jolt upwards S waves Secondary waves Arrive second Longitudinal waves Shake back and forth Surface waves Move the slowest, arrive last Make the ground move like ocean waves Often causes the most destruction

How do we detect earthquakes? Devices called seismographs detect shaking Larger amplitude means larger earthquake

How do we know how big it was? Magnitude- unit of measurement for earthquakes Different Scales Mercalli Based on amount of damage Richter Based on the earthquake’s size Accurate for small earthquakes nearby Different depending on distance from epicenter Moment Magnitude Measures the total energy released by an earthquake Most accurate Used by scientists today

Magnitude 2.5 or less Usually not felt, but can be recorded by seismograph. 2.5 to 5.4 Often felt, but only causes minor damage. 5.5 to 6.0 Slight damage to buildings and other structures. 6.1 to 6.9 May cause a lot of damage in very populated areas. 7.0 to 7.9 Major earthquake. Serious damage. 8.0 or greater Great earthquake. Can totally destroy communities near the epicenter.

How do we know where the epicenter is? Location: Triangulation We know how fast different waves move, so we can calculate how far away the earthquake was by the amount of time between arrival of P waves and S waves We use at least 3 locations to find the location of the quake

Triangulation Practice http://www.geology.ar.gov/pdf/Locating_an_epicenter_activity.pdf

Earthquake Hazards Ground shaking Surface rupture Landslides/rock fall Causes damage to structures Surface rupture Offset of the ground surface Landslides/rock fall Occurs on steep slopes (M4.0 and larger) Shaking causes hillside to break loose Flooding Due to broken pipes, failed dams, or result of tsunami or seiche Fire Usually caused by ruptured gas lines or arcing power lines Ground shaking Surface rupture Landslides/rock fall Flooding Fire Tsunami/Seiche Liquefaction

Seiche and Tsunami Seiche: standing wave in an enclosed or partially enclosed body of water Tsunami: a wave train, or series of waves, generated in a body of water by a disturbance that moves the whole water column

Liquefaction Liquefaction is the mixing of sand or soil and groundwater during the shaking of a moderate or strong earthquake. When the water and soil are mixed, the ground becomes very soft and acts similar to quicksand.

Wasatch Fault One of the longest and most active normal faults in the world, the 240-mile-long Wasatch fault extends from Malad City, Idaho, south to Fayette, Utah. It is subdivided into 10 segments, averaging 25 miles in length Segments rupture independently Nearly 80% of Utah’s population lives within 15 miles of the Wasatch Fault

https://earthquake.usgs.gov/hazards/qfaults/map/#qfaults https://earthquake.usgs.gov/scenarios/eventpage/uulegacyshakeoutf f_se#executive

Preparation https://www.utah.gov/beready/documents/roots_earthquake_low.p df

Volcanoes Volcanoes can occur at three types of locations: Diverging Boundaries Mid-ocean ridges Converging Boundaries Island arcs- Japan, New Zealand, Aleutian Islands Oceanic-Continental collision: Andes Mountains, Cascade Mountains (Mount St. Helens) Hotspots An extra hot plume from the mantle causes melting and magma to build and erupt in a mostly stationary location Hawaii Yellowstone

Magma Viscosity- the resistance of a liquid to flow High: gloopy Low: runny Silica- particles made of silicon, most abundant material in Earth’s crust Makes magma more viscous Carbon dioxide- dissolved in magma (like soda) Causes magma to rise and erupt

Types of Eruptions Energy Transfer- Heat to Mechanical Quiet Explosive Low silica= low viscosity Lava pours from the vent or cracks Example: Hawaii Explosive High silica= high viscosity Builds up in the volcano’s pipe and builds pressure When pressure is released, trapped gasses rush out, causing a violent eruption Example: Mount St. Helens

Volcanic Hazards Lava Flow Pyroclastic flow “Bombs” and rock fragments Ash fall/acid rain Landslide Mud/debris flow Fumaroles/ volcanic gases https://pubs.usgs.gov/fs/fs002-97/

Severe Weather Thunderstorms Tornadoes Hurricanes Blizzards Floods http://www.nssl.noaa.gov/education/svrwx101/ US Deaths Due to Severe Weather

Predictability Time Location Magnitude Time: Location: Magnitude: Some hazards are proceeded by “warning signals” Location: Hazards require certain criteria to occur Magnitude: Based off previous events and data for current situation