Class Notes

Weathering

    There are two types of weathering, physical (also called mechanical) and chemical.  Physical weathering merely breaks down the material into smaller and smaller pieces.  These pieces are still recognizable as to their source rock.  Chemical weathering actually changes the chemistry of the material.

TYPES OF WEATHERING

    mechanical (physical)

        freeze and thaw (frost wedging)
        salt wedging
        unloading
        thermal expansion
        biological (also a form of chemical, but most
             weathering is by mechanical)

    chemical

        solution  (dissolved load of stream transport)
        hydrolysis
        oxidation

    soils horizons

        O horizon (humus - organic material)
        A horizon (zone of leaching)
        B horizon (zone of accumulation, the material
             from A horizon)
        C horizon (regolith - decomposed parent
             material)

    soil types

        pedalfer (high rainfall, rich in iron and
             aluminum}
        pedocal (rich in calcite, low rainfall)
        laterite (most everything soluble is gone)

General: All hills are moving and being pulled down. This is done by gravity. Hills are in a delicate balance between the moving force at the top and the resistive force at the bottom of the hill. The resistive force is holding up the hillside. Disturb it and the hillside becomes unstable.

Mass wasting is the second process involved in the destruction of our topography. The first was weathering. Mass wasting moves material down slope to appoint where it can be transported by water, ice or wind.

Fall Ice wedging typically creates unstable loose pieces of rock which then fall. You have seen this when you see rocks at the base of cliffs in the mountains. This event frequently occurs during the colder period of the year.

Slump also called a rotational slump, it is a type of slide that involves a thick layer of material. The plane of failure is a curved surface, convex upward. These events typically happen in the summer time and are self stabilizing. They cause considerable damage but little injury as they are readily predictable.

Slide also called a translational slide. This event is caused by sedimentary beds dipping out of the slope of a hillside. Such beds are said to be day lighted because the ends of the beds are exposed to day light. This exposure means that there is no resistive force holding the beds up. Water getting on the bedding plane lubricates the clay layer found there and the material above moves down slope.

Flow this is a surficial event involving only a typically thin layers of material. Large amounts of water are required for this event to occur and therefore they occur during rain storms. As such they cause considerable injury because most are indoors during the rain and do not see the impending disaster.

Creep this is a slow moving event caused by freeze and thaw of surficial material or the hydration and dehydration of the surface material. In any event it caused the material to move down slope. It is so slow moving that there is no injury associated with this but since all slopes are creeping considerable damage is done.

Since water is one of the most common destabilizing forces we need to keep the water off the slope and out of the slope. This can be done by covering the slope with tarps, temporary, or gunite. We can drill wells into a slope to allow water to percolate out of the slope or to be withdrawn by pumping.

We can buttress the resistive force by adding material to the base of the slope.

Building codes for hillside development have requirements for the allowed angle of the slope

We add mass to the top of a slope, such as a building or swimming pool. We over steepen slopes by cutting into them for a house pad or road.

We remove the toe of the hillside, the resistive force, for housing pads or roads.

Chapter on Earthquakes

Earthquakes are caused by the sudden release of accumulated stress.  As stress accumulates it changes the shape of the surface of the earth, this is strain.  After the earthquake, the two sides snap back to their original shape, this is called elastic rebound.

The earthquake starts at the focus, also called the hypocenter.  From this point of origin, two seismic waves are generated and the same time, the P wave and the S wave.  These waves move through the body of the earth and are called body waves.  When these waves reach the surface of the earth, called the epicenter, they then generate two more seismic waves that travel along the surface of the earth and are called the surface waves.  The surface waves do the most damage during an earthquake.  The P wave moves in a push-pull manner and the S wave moves as a jump rope.  The surface waves move like Willie Wonka's Wonkavator, in all directions.

We can calculate the distance to the epicenter from where we are because the P and S waves leave the focus at the same time and travel at different speeds.  Thus the lag time, time between the arrival of those two waves indicates the distance to the epicenter.  We know that at 100 km the lag time is 8 seconds.  It takes three instruments at a station to completely measure the movement of an earthquake and it takes measurements from three stations to locate the epicenter.

The modified Mercalli intensity scale indicates the amount of damage done during the earthquake and how people reacted to it.  this is a closed scale because magnitude XII is total destruction.  The Richter Magnitude Scale gives an indication of the intensity of ground shaking and the amount of energy that is released.  This scale is commonly used today for press reports but is inaccurate for large earthquakes.  For large earthquakes we use the Momentum Magnitude Scale that includes all of the information used in the Richter scale plus the area of rupture.  The Richter scale is logarithmic.  Thus the difference in intensity of shaking between any two points on the scale is 10.  Similarly the difference in the amount of energy released is just larger than 30.  There is an illustration in your textbook showing the use of the Richter Scale nomograph to calculate the Richter magnitude of an earthquake.  You should know how to do that.

Earthquakes cause hazards.  1) is disease, in our case a fungus in the soil that causes Valley Fever, which can be fatal.  Use a surgical mask for protection.  2)  then there is fire.  You should strap your water heater at the top and bottom ;using plumber's tape, to the wall.  If you smell gas leave the premises and phone for help from another location because light switches and phones are potential point sources of ignition.  3) Things falling on you are dangerous.  You can use velcrow straps for large items and museum putty for smaller knick nacks. 

Chapter on Volcanoes

Volcanoes are the end product of rising magma.  As it rises, volatiles are released from solution so that the liquid rock that comes to the surface of the earth, called lava, is different chemically than the liquid rock underground, called magma.

the precursors of a volcanic eruption are first, earthquakes, leading to harmonic tremors or D-type earthquakes.  Then we have gasses coming to the surface, particularly SO₂.  And finally the inflation of the volcano itself as magma fills the magma chamber.

There are basically two types of volcanic eruption, a quiet one and a catastrophic one.  the difference is caused by temperature, amount of volatiles, and the amount of Silicon it holds,.  Higher temperature is lower viscosity.  More volatiles makes it more viscous and more silica makes it more viscous.

The types of volcanic mountains formed depend upon the type of eruption.  Quiet eruptions produce shield volcanoes composed of essentially all lava flows, hence their large size and flat shape.  Catastrophic eruptions form composite or strataform volcanoes, intermediate in size and the shape that all recognize as volcanic, which are composed of alternating layers of pyroclastics and lava.  Cinder cones, composed of all pyroclastics are the smallest form.

;there are several hazards from volcanic eruption.  They include lava - divert it; ash in air for planes - divert them; ash in air breathing it in - use a mask; ash on the ground, lahar, - divert it; ash on the ground roofs collapsing - don't go in house; climate change - adapt; tsunami - go up slope; pyroclastic flow (nuee ardente) - leave when warned.  Except for the lava flows, virtually all of the hazards are from catastrophic eruptions.

Chapter on mineral wealth and energy

All resources important to us need to be concentrated in order for their exploitation to be economic.  Remember the differences between renewable and nonrenewable resources.

Mining Act of 1872 was to encourage people to go west and discover and exploit mineral wealth for the good of the country.  therefore there was no royalty payment to the government nor environmental regulations.  You only had to do $100 worth of improvements per year.  Today we would change that to have royalty payments to the government plus environmental rules.  Remember that in the later 1800's mining was a small operation that could cause little problems.

Fossil fuels and other forms of energy production that are used today as used because of their economics.  Yes, we do not add in the cost of environmental damage, but even if we did they would still be cheaper than the alternatives. l Technology offers a hope of reducing the economic penalty of alternative sources of energy, but it doesn't always move at a pace that we would want it to.

Petroleum is found in both conventional and nonconventional occurrences.  We are running out of conventional deposits of petroleum.  But we do have some unconventional deposits that contain huge quantities of petroleum.  One is the tar sands of Canada.  the draw back to these deposits is the sand that is the waste product, it is fine and gets into transmission and wheel bearings.  Secondly is the oil shale (not an oil or a shale) of western Colorado and eastern Utah.  the draw back to these is that it takes 2 barrels of water to make one barrel of crude, in an area with little surface water.  Also the marl expands upon heating and therefore you are faced with disposing of 112% of the volume you take out of the ground.

Natural gas is a similar nonrenewable resource, but we have more of it than crude.  Nonconventional sources of methane are coalbed methane and hydrates.  The problem with hydrates is that you have to heat them and may being heating and melting ice outside of your containment area.  The coalbed methane has some environmental problems with the disposal of water.  But coalbed methane does produce with a positive decline curve and is therefore much more economic.

Hydroelectric power can be the least expensive form of energy.  Once you have built the dam there is only maintenance.  But there is severe ecology damage due to dams.  You are flooding valleys, many of which were crop lands, thus reducing the arable land.  You are destroying ecosystems, interfering with the migration of fish, many of which are of commercial value.

Wind power, a form of solar power as the wind is caused by the heating by the sun of different parts of the earth's surface.  Unfortunately, most of the areas that have steady winds of 20 mph are also flyways for migratory birds.  During migration periods we have found that the death toll of birds is truly staggering and we need to turn the windmills off.

Passive solar power, where the sun heats a wall or confined water on a roof top can be competitive.  However, generally our roofs are not designed for the weight of the water, the tubing frequently gets plugged with bacteria, and the technique is not useful on cloudy or rainy days.

Active solar conversion of sunlight directly to electricity, or photvoltaic systems, are not ;yet cost effective and find most use in remote situations.

OTEC, the conversion of temperature differences in water at depth to surface waters to electricity has not proven to be economic.  However, there are advantages from this in other areas.  The cold water, when used in aquiculture, provides a disease free environment.  The cold water, when piped under pineapple plants has led to more than one growing season.

Nuclear power has some advantages, but the disposal of waste is a leading drawback.  Remember the "China syndrome", which, as I explained could not happen.