Geology Part Two: Natural Disasters

by Amy Jaecker-Jones


As a child, we practiced "duck and cover" drills in school. At home, the slightest bit of shaking would send me running to the nearest doorway. The very possibility of, "THE BIG ONE" happening in my lifetime, had 8-year-old Amy making plans for a move to Florida.

Natural disasters are a fact of life, not just in California, but everywhere. They include powerful forces of nature, cause serious devastation, and remain in our memory and imagination long after the actual events have taken place. Mount Vesuvius erupted in 79 A.D., and we're still talking about it. Such is the mythic appeal of that event that an exhibition of artifacts tours the world. Recent events, such as Hurricane Katrina and the series of Japanese earthquakes, which caused both a tsunami, and the Fukushima Nuclear Power Plant disaster have had a profound influence on our collective conscience. They've renewed conversations about racism, social justice, urban planning, and the safety of nuclear power plants.

Professor Joe Holliday, of El Camino College's Earth Science Department, makes a special study of natural disasters, and he shared his knowledge with students in the California Naturalist Program at the Dominguez Rancho Adobe Museum.

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When we discuss earthquakes, the term, "fault," usually enters the conversation. A fault is a crack in the earth's crust. It may align with a transform plate boundary as in the case of the San Andreas Fault, but in most cases, a fault is not along a plate boundary. (For a discussion of plate boundaries see the previous post - Geology Part One.) A fault can be very small or so large that it is visible from space. The area of land between faults is much less than that covered by plates. Fault areas only span 20-30 miles. An earthquake occurs when there is a sudden movement along the fault. This movement is described in three ways: extension (normal), compression (thrust, reverse), and transform (strike-slip).

An extension fault is where two sections of crust pull apart, forming a valley in the gap. The Basin and Range province of California includes an example of an extension fault. The Transverse Ranges of southern California are examples of compression fault activity, in which one block of crust slides on top of another, often forming mountains. In contrast, transform faults, such as the San Andreas, do not show much vertical movement. Instead, opposing blocks of crust slide past each other. In California, Professor Holliday said, compression faults generally occur north of Interstate 10; extension faults occur to the south.

Earthquakes reveal weaknesses in our infrastructure. The 1933 Long Beach earthquake set new standards for building. Earthquakes in Whittier and Northridge both occurred along previously unknown compression faults. A friend of mine describes house sitting during the Northridge earthquake. She had to call the homeowners and tell them to return because, "their pool was in the living room." I remember driving up to Sacramento that same year and taking a picture of a collapsed portion of the 5 freeway. Professor Holliday's faculty page at El Camino College shows many examples of buildings damaged in these two earthquakes.

Damage to the 5 freeway following the 1994 Northridge earthquake.

What are the dangers?

 

In addition to lives lost, "THE BIG ONE," when it comes, will cost hundreds of billions of dollars in damage to housing, commercial buildings, and infrastructure. The last time in recorded history that the San Andreas Fault moved in a major way was in 1680. We are overdue for another major earthquake.

Liquefaction is a risk in flood plains and harbor areas where the ground is saturated due to a high water table. When liquefaction occurs, the ground experiences a decrease in strength and stability, causing buildings and other structures to lose their foundational support. The depth of a basin correlates to the amount of shaking experienced in that region. The Los Angeles area's sediment is five miles deep. Therefore, areas at risk of liquefaction will also experience five times more shaking, for five times longer than other areas. Because liquefaction zones commonly occur along the coast, where our nation's most important shipping ports are located, earthquakes may cause a significant economic impact that goes beyond the cost of damages and repair.

Landslides may occur in areas where sedimentary rock is steep. Slides may occur quickly or slowly. A slump landslide is one which happens slowly and has the potential to move houses and shut off traffic.

What should we do?

 

Proponents of an early seismic warning system are on the right track. Construction of such a system is an expensive option, but one that is truly vital to the health and safety of California's residents. Fortunately, in 2014, Congress approved $5 million for this purpose. According to the Los Angeles Times, the system may be available to some schools, fire stations, and private businesses later this year. Eventually, scientists hope, the general public will receive notice of an impending earthquake seconds before shaking begins. Notices would arrive via cell phones, computers, and specialized weather radios. Mere seconds may not sound like much time, but it might mean the difference between life and death. An early warning system would allow people to find safe places to shelter, fire stations to open their doors before power outages occur, construction firms to stop heavy equipment, and for rail systems to stop or slow trains.

Save your precious belongings!

Prepare! Prepare! Prepare! That's good advice in any context, but especially in relation to earthquakes. Professor Holliday says that he makes a habit of walking through friends' houses, demonstrating how many loose objects would fall or fly in the event of an earthquake. I admit, I've been looking at my own house, and assessing how unsafe it might be. Much of our heavy furniture and picture frames are bolted to the wall, but not all of them. Additionally, I have too many small items sitting on shelves and tables that I could secure by using an adhesive such as museum putty, wax, or gel. Like many other parents, when our baby years were past, my husband and I removed the cupboard and drawer locks in our kitchen. I've been thinking about putting them back to prevent all of our dishes and pantry items from ending up on the floor. An even simpler approach, is to follow my grandmother's example of wrapping rubber bands around cupboard door knobs to prevent their flying open.

My grandmother's simple safety measure.

One major improvement that homeowners can make is to bolt their houses to the foundation. For many modern homes, this might already be done. I live in an old house which is not bolted to the foundation. Years ago my husband and I researched having a company provide this service, and for reasons I cannot remember, opted not to have it done. Perhaps we were worried about cost. Although this sounds like an expensive fix, according to Professor Holliday, it can be done by homeowners themselves without spending a lot of money.

Professor Holliday advises putting together a household survival kit. Pack food, water, medicine, and first aid supplies. Also include fix-it directions for common household problems. Do this BEFORE an emergency happens. Electric, gas, phone, and internet connections may not be available in the days immediately following an earthquake. Additionally, grocery stores will most likely be closed, partially for the reasons described above, but also for clean up. Professor Holliday said that following the Whittier earthquake, many items fell off grocery store shelves including food, alcohol, and household chemicals. These items combined to form a toxic mess.

We are a car culture. Many of us commute more than an hour to work every day. What happens, Professor Holliday asked, when an emergency occurs that threatens to strand us at work? If the roads themselves haven't been damaged, they are certain to be jammed, and you may find yourself walking home. He recommends keeping a pack with you, which contains walking shoes and water. If you wish to add to your pack, there are plenty of websites which will help you to select useful items.

In addition to earthquakes, what other types of disaster might we face in California?

 

Perhaps you've heard of the "100 Year Flood?" It's gained some press attention in recent years. According to Professor Holliday, a major flood will have the same death toll as a major earthquake but occur over a longer time period. Personal property damage from flooding will also be greater in the event of a flood as memorabilia, important documents, carpets, and walls are all damaged or destroyed by high levels of water.

We don't usually think of our state as receiving enough rain to cause major flooding, especially not in these days of drought, but the danger exists. Concentrated moisture flows through the atmosphere in "rivers." Atmospheric rivers can cause continuous rainfall for up to a month. One of these storm systems arrives in California approximately every 100 years. They can occur in northern or southern California. The last time the state experienced such large-scale flooding was in Los Angeles and Anaheim in 1938. Currently, we do not have the capacity to handle a major long-term flood situation. Existing reservoirs would fill quickly, and the ground become too saturated for water to percolate into underground aquifers.

Fortunately, urban planners seem to be aware of the potential risks of flooding and are incorporating their ideas into disaster plans. Most people, however, are not prepared for flooding, especially for one of such magnitude. Many of the same precautions recommended for earthquakes can be applied to flood preparation. In addition, it is wise to invest in water-safe containers for important items and to store your most beloved belongings in the upper sections of a room or house.

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As you might have guessed (because I am part of the California Naturalist Program), I did not follow 8-year-old Amy's advice to move to Florida. I'm still waiting for "THE BIG ONE." Hopefully I (and you) will be prepared when it comes.



References:

Holliday, Joe, "Soils, Geology and Weather" (lecture, California Naturalist Program, Rancho Dominguez, CA, January 31, 2015).

Lin, Rong-Gong II. 2014. "California Receives U.S. Funding for Earthquake Early-warning System." Los Angeles Times, December 14. http://www.latimes.com/local/california/la-me-quake-early-warning-20141215-story.htmlhttp://www.latimes.com/local/california/la-me-quake-early-warning-20141215-story.html

Oskin, Becky. 2014. "Fault Lines: Facts About Cracks in the Earth." Livescience.com, September 25. http://www.livescience.com/37052-types-of-faults.htmlhttp://www.livescience.com/37052-types-of-faults.html

Geology Part One: Digging Beneath the Surface of California

by Amy Jaecker-Jones


One of the pleasures of being in the California Naturalist Program is hearing from its faculty of diverse and highly educated instructors. Geology Professor Joe Holliday is no exception. Professor Holliday teaches in the Earth Science Department at El Camino College and travels as a naturalist for the National Geographic Society. During his lecture, he discussed the movement of the earth's plates and how that movement relates to the type of soil and topography found in California. He also spent time exploring one of his favorite subjects - natural disasters.

Part one of this series on geology will deal with what happens beneath the surface of California.

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The earth consists of a solid inner core, a molten outer core, a ductile mantle, and a comparatively thin crust. Some readers may remember making Play-Doh models with separate colors to designate the core, mantle, and crust.

Actually, Play-Doh is a wonderful metaphor for the inner-workings of the earth, and one that Professor Holliday particularly likes to describe the mantle. Like me, you may have thought about the mantle, and imagined it to be a liquid layer of red-hot lava. It is not a liquid, however, but a solid that moves.

Take a moment to remember the feel of Play-Doh in your hands. It's solid. It can take a definite form. If you turn your hand sideways, it won't drip. But it's not like other solid materials which must remain in one shape. You can squish it. You can squeeze it. You can re-form it again and again. It is this ductile quality of the mantle and the movement of tectonic plates above it that allows the surface of the earth to be constantly re-forming.

On top of the mantle lies the earth's crust. The crust is made up of different plates that move under, over, and against each other. There are three types of plate boundaries, and California is distinguished by having all three active within its borders. For this reason, it is worth learning a little about each type of boundary.

• Divergent plate boundaries primarily occur in the ocean. As the mantle moves, lava begins to rise. It seeps through cracks in the crust and spreads the two plates apart, creating new land in the process. This continuous process of spreading could continue without ceasing if it were not for the next two types of plate interactions.

• Convergent plate boundaries may be oceanic or continental. In the case of an oceanic plate colliding with a continental plate, the thinner, heavier oceanic plate bends under the continental one. The result is a rise in the continental plate. The oceanic plate, now forced underneath the continental plate, begins to melt. As it melts, some of the magma rises again and exits the crust through a volcano. In the case of two continental plates coming together, there is not enough difference in their weight for one plate to bend under the other. As a result, they smash together. Hot rocks become welded to each other. Some magma rises and cools to become mountains. The rest of the magma is pushed downward into the earth.

• Of the three types of boundaries, transform plate boundaries are the most important in California. This type of boundary is the primary cause of earthquakes. The San Andreas Fault is our most famous example of a transform plate boundary. Transform plate movement is also responsible for creating California's Central Valley, a sunken area, surrounded by tall mountain ranges. Unlike other plate boundaries, transform boundaries do not involve magma. Two continental plates move past each other, but instead of sliding smoothly, they grind against each other and get stuck. Then with a jerk, they move some more. Every 200 years, approximately, the movement is jerky enough to cause a major earthquake. To a person standing near the epicenter of one such extreme quake, the sound would be similar to that of an airplane crash.

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I learned one fact in this lesson that threatened to change the way I see myself as a Californian. Perhaps, for you, it will only be an interesting bit of trivia, but for me, it was shocking. In geologic terms, according to The California Naturalist Handbook, much of California is not a part of North America. Everything to the west of the San Andreas Fault sits on the Pacific Plate. As the name implies, the Pacific Plate is mostly covered by ocean. In fact, the only part of the earth's crust that sits on the Pacific Plate is in western California. All the land to the east of the San Andreas Fault, including the entire rest of the country is on the North American Plate (de Nevers, Edelman, and Merenlender 2013, p.32-33). Suddenly, reading that fact, I didn't know who I was anymore. I thought I knew my place in this world. I live in: Los Angeles County, southern California, in the western United States, on the continent of North America. As for my geography and nationality, this understanding is still true. But geologically, I live somewhere else. My house sits on the Pacific Plate.

However, despite years of jokes, California is not physically apart from the rest of the country. If I drove out to the San Andreas Fault, I might see a jagged line of demarcation, but I would not see a bottomless gap dividing the Pacific and North American Plates. The landmass that I live on is indeed part of North America. The separation between plates occurs 10 miles beneath the surface. The next part of this series will discuss what happens when the San Andreas Fault begins to move as well as other potential natural disasters.


References:

de Nevers, Greg, Deborah Stanger Edelman, and Adina Merenlender. 2013. The California Naturalist Handbook. Berkeley: University of California Press.

Holliday, Joe, "Soils, Geology and Weather" (lecture, California Naturalist Program, Rancho Dominguez, CA, January 31, 2015).