Week 8: Mass Wasting Events

 

This week we are discussing 'mass wasting' events...aka, landslides, mudslides, rockslides, etc. These are very related to flooding and rain events and very frequent!- just last Sept a 300 to 400-foot section of bluff along the coast of southern Los Angeles County collapsed, damaging properties known for their coastal erosion problems (news). You are also familiar with the recent avalanche near Tahoe that killed 9 people 

These hazards are connected to others like earthquakes or flooding or wildfires.... although mass wasting events do not need any triggers (just gravity!). As an example, a 7.3 magnitude earthquake hit NE Japan and provoked several landslides and rockslides (image below).

Landslides in the United States cause approximately $3.5 billion in damage and kill between 25-50 people annually. The US Landslide inventory map below shows these hazards widespread within the country.

The largest landslide in modern U.S. history (in terms of volume) was most likely one that occurred in 2013 in Bingham Canyon outside of Salt Lake City, Utah. It had a slide mass of 55 million cubic meters (compared to an estimated 10 million cubic meters during the Oso event in 2014).

Landslides impact California’s terrain often. These are generally related to precipitation patterns, in particular if there has been previous months of drought conditions. In January 2019, Pacific storms brought a lot of rainfall to the state. The heavy rain forced residents to evacuate from wildfire-ravaged areas. The “high risk” areas for mudslides are so because they are adjacent to steep slopes or are located at the base of drainage areas. Recent examples are the ‘Woolsey’ and the ‘Hill’ fire burn areas, which will be subject to high volume of mud and debris flow moving forward. The website of California Landslide response is a great place to find information! 

If you want to know more about these hazards, the USGS page has also great information on how to identify landslides and what to do if one happens. If you want to know if you are living in a risk area, you can access maps like the USGS below that shows the Emergency Assessment of Post-Fire Debris-Flow Hazards.

One of the best ways to mitigate this hazard is being aware of the soil we build on and plan accordingly. The thinkhazard site has very good recommendations as well.

Stay informed and safe-

Week 5: Volcanoes

 There are about 169 volcanoes in the United States that scientists consider active (source). Most of these are located in Alaska, where eruptions occur virtually every year. Others are located throughout the West and in Hawaii (Ring of Fire anyone?). 

There are several ways we minimize the danger of volcanic activity (apart from the obvious of ‘getting out of the way’…(:

·         Forecasting (earthquakes as early warnings -although a Japanese volcano erupted without any previous seismicity (livescience article), land swelling before eruption, gas emissions, etc.)

·         Volcanic Alert Codes (USGS): the levels of alert and the aviation code levels commonly change at the same time (chart on right). A non-erupting volcano will have a green icon, and a red one indicates an imminent eruption (see USGS Alert Codes).

Today the US USGS hazards map (images below) shows 4 volcanoes as to be above normal background (elevated unrest):

Kilauea and Great Sitkin, Alert Level= WATCH. Aviation Color Code = Orange.

Shishaldin and Ahyi Seamount, Alert Level= ADVISORY. Aviation Color Code = Yellow

Note: If you want to know more about volcanoes and how we monitor them, there is a MOOC from the University of Iceland you might want to enroll into. A short video explanation here. 

Week 3: Earthquakes

 We are exploring earthquakes and what countries do to prevent/mitigate the hazard. If I want to know something about earthquakes in a place, the first websites I go to are: the USGS Real Time Earthquakes Website or the IRIS monitoring website.

Regarding where quakes are located in the US, the seismicity map below from USGS shows the (obvious, in red) ring of fire portion on the West coast but also a central area in the middle of the plate. I’d like to talk a bit more about this non-obvious one. This area, called the New Madrid Zone was shaken by a M8(!) in 1811. The reason for the activity is a very old intraplate rift placed below the area (see image from http://showme.net).

The San Andreas Fault System is responsible for most of California natural quakes...Each year the southern California area has about 10,000 earthquakes.!! The latest swarm of quakes in the Salton Sea has been featured in the news often. Earthquakes up to magnitude 4.6 under the Salton Sea are raising concern that a larger quake could be unleashed on the San Andreas fault. The southernmost section of the fault has not ruptured since about 1680.

So, what can we do about it?; apart from the obvious need for education, I want to focus on the USGS ShakeAlert system, developed for the West coast using some of the existing systems. Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of an EEW (Earthquake Early Warning) system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm’s way. Studies of earthquake early warning methods in California have shown that the warning time would range from a few seconds to a few tens of seconds, depending on the distance to the epicenter of the earthquake. 

There is an Earthquake Tracker all Californians can download to keep informed: try My Shake App.

A few seconds of warning could make all the difference (enough to stop transit/elevators and to drop, cover, hold on).This year's International ShakeOut Day is October 15, when millions of people worldwide will participate in earthquake drills at work, school, or home!

Being aware of the risk and know what to do when the shaking starts is very important. We know that earthquakes cannot be predicted (I recommend Dr. Jones’ book called the big ones’ if you want more information about that)

Week 2: Plate Tectonic Boundaries Exploration

 This week we are exploring Plate Tectonics and how important it is to know the location of the plate boundaries, and how it is closely related to some natural hazards, like volcanoes or earthquakes.

In the US, the NOAA map below shows how the Easter part of the States is a passive margin, and the Western side of the country is a very active one, with the Pacific Plate, Cocos, Juan de Fuca plates connecting to the North American plate. Not a surprise we are on the ‘Ring of Fire’, where a lot of the volcanic and seismic activity happens!

Closer to home, the transform plate boundary called SAF (San Andreas Fault) is responsible for most of the shaking. These plates (North American and Pacific) are slowly moving past one another at a couple of inches a year; about the same rate that your fingernails grow! Our amazing SAF is also a right strike slip fault. 

Of course, there are a few exceptions, like the activity of Hawaii within the Pacific plate (hot spot) or the New Madrid area (ancient rift) within the North American Plate, both not at plate boundaries, but that will be another post another time...

We might not know when events like volcanic eruptions or big earthquakes will happen (a lot of these happen underwater...), but if you know your Tectonics, you definitely know WHERE they (mostly) do!