Channel straightening

increases gradient water drains quickly,
disadvantages - results in more sever flooding down river.
expensive
reduces soil moisture
also slow down rain water going towards sea
disadvantages:
requires large areas of land that will be unavailable for other uses.

deepen+widen channel:
excavation + dredging equipment increase channel size. concrete slabs help reduce friction on river bed improving efficiency of flow. increases discharge flor through channel.
disadvantages:
expensive
creates problems downstream due to increased discharge

artificial levees:
build up river banks using earth + rock increases discharge capacity.

discharge:
expensive
can create problems downstream if breached = massive flooding as river level is much higher than surrounding flood

overflow basins:
designated area of floodplains allowed to flood

dams:
built along tributaries and the main river channel less water released into river during periods of heavy rain. this prevents discharge from rising too much. reservoir levels are increased instead.
Disadvantages:
expensive but can help produce electricity and provide regular water supply.

Case study - mississippi

Mississippi - the Facts

The river basin is the fifth largest in the world

It is the third longest river in the world behind the Nile & the Amazon

The river discharges 584 million tonnes of sediment a year

The flood plain is 200km wide at its widest point

The Mississippi flows through 10 states

The river carries 13% of all freight traffic in the USA

Its main tributaries are the R. Ohio, R. Kansas, R. Missouri & the Red River



The Causes of the 1993 Flood

Floods are normal in the mid-west - usually arriving in the spring when rain and snowmelt fill the streams & rivers that drain the upper Mississippi Basin

In 1993 as normal this happened - the soil was still saturated from spring rains. Normally this is followed by dry weather &has done so for the last 20 years

In 1993 Atmospheric conditions conspired to bring further torrential rains to the Mississippi Basin




a. A Jet stream swung South bringing Cool dry air
b. Warm air moved North causing Thunderstorms
c. Two high pressure systems developed blocking any movement of the thunderstorms
d. The rains continued throughout May, June and July.



Human Causes of the 1993 Floods

Urbanisation of the Flood Plain - reducing infiltration rates etc

Poorly built non-federal levees

The development of unsuitable sites for development

The channelisation of the river - especially at St Louis

The 1993 Flood Fact File

Primary Effects

50 people died

62,000 families were evacuated

72,000 homes were flooded

70% of levees were damaged

55 towns were wrecked

6 million acres of farmland was flooded



Secondary Effects

River traffic halted for several months

Crop losses were put at $2.6 billion

Insurance pay-outs reached $12 billion in property alone

Stagnant water attracted mosquitoes and rats and there was a threat of disease

Electricity lines collapsed leaving many towns without power





Holding back the tide with sandbags

Transport - Roads and Bridges affected





Response to Flooding on the Mississippi

Dams & Reservoirs - 6 huge reservoirs have been built along the River Missouri to store excess water with a further 19 along the Tennessee River and its tributaries

Afforestation - The Tennessee Valley Authority has been increasing tree cover to delay run off into rivers

Levees - Have been strengthened with concrete mattresses to reduce erosion of the river banks

Diversionary Spillways - These are overflow channels which can store excess water in times of flood and release it after the risk of floods have passed

FEMA - The Federal Emergency Management Agency has published risk assessments and encourages at risk settlements to move off the flood plain

Flood Forecasting - The National Weather Authority are now responsible for flood warnings along the river

There are of course more - remember to look at your own case study notes

Mississippi

1993 - mississippi burst its banks.
150 levees collapsed
dam burst - bridges closed
by July mississippi spread between 10 - 25 km

Effects:
9 states affected
23million acres covered 48 killed
26.5m sandbags used
70000 evacuated
final damage cost 10 billion US dollars (25% crop losses)
Town of valmeyer abandoned
River closed for 2 months (15% freight uses river)

Climate prior flood:
Heavy rain due to high pressure over bermuda
torrential rain June/July added to water level most water in 2 months since 1895

Taming mississippi:
- Vital Transport route
- Wing dykes
- Straightening
- 1600km of levees
- Many dams
- Much of river lined with concrete slabs

engineers caused floods
1993 worst flood ever despite engineering

- shortening the river caused it to flow more quickly increasing erosion
- restricting flow inside levees speeded up flow and increased pressure on levee. 1993 a large no. of levee's broke
- altering natural flow created bigger flood despite less water in the river than previous floods
- Increasing energy in river reduced sediment movement.

Causes of floods

- heavy Rainfall
- snow melt and heavy rainfall
- Deforestation
- Urbanisation - Garbage
- Soil Saturation

Useful Terminology

Delta
A large fan-shaped area of silt deposits found at the mouth of a river where it enters a sea or lake. A triangular area of deposited silt or alluvium at the mouth of a river. It will occur where a river carries a heavy load and empties into a shallow sea. As the area of silt increases the river tends to divide into many smaller channels.

Lagoon
A body of shallow water of varying salinity wholly or partially separated from the sea by some form of barrier, such as a sand bank (or reef).

Bottomset beds
Layers of the finest load (clay) that is deposited at the seaward edge of the delta. These particles are transported by suspended load being carried out the furthest by the river and are deposited when the river has little or no remaining energy at the seaward edge of the delta

Foreset beds
Layers of bedload, including the largest sediments (pebbles & sand) that roll along the river channel. The bedload rolls over the edge of the delta and builds up a steep angled layer on top of the bottom set beds as the main delta advances. These course materials at the advancing front of a delta form the bulk of the delta.

Topset beds
Horizontal layers of smaller sediments (silt & clay) that overlay the foreset bed. The suspended load settles out into horizontal beds over the top of the delta.

Class notes

flood hydrographs

-

ACTIVITIES PAGE 15:

1a) on picture.
b)i - February. ii - February.
c) Because there is more rain in the winter than in the summer.
d) Because while there was no rain the water was still running off.

2.a)i - 5 hours.
ii - 4 to 5 am.
iii - 9 hours.

b)i - The time it takes to begin to discharge.
ii - Because the next storm stops it from falling.
iii - Because there was more precipitation and because it went on for longer.


c) The water would have over flown over the banks and flooded the surrounding area.

Flood Plains

Delta Formation:
Delta are found at the mouth of the river, where the river meets the sea. at this point the river is carrying too much load for its velocity and so deposition occurs. The top of the delta is a fairly flat surface. This is where the coarsest river load is dropped. The silt is dropped to form a steep slope on the edge of the delta hile the clay stays in suspension until it reaches the deeper water.

Different Delta's:

Accurate Delta:
- triangular/fan shaped
- water enters the sea through many distributaries
- formed when alluvial (rich soil) deposits are even spread out
- long shore currents help to form spits and lagoos at the mouths of the distributaries
- e.g.: nile delta

Bird's Foot Delta:
- has distributaries that extend far into the water
- formed when river discharge is high and load is enormous
- sediments deposited far exceeds those removed by tides and currents
- e.g.: mississippi delta

Estuarine Delta:
- sediments are deposited in a long narrow submerged estuary
- delta does not usually grow beyond the general coastline because sediments deposited outisde the estuary would be washed away by waves and currents
- e.g.: seine delta

Cuspate Delta:
- tooth shaped or pointed delta formed by one dominant channel carrying most of the sediments out to sea
- e.g.: ebro delta

Formation process of Deltas:

- when a river enters the sea, it mixes with the surrounding water and its speed is reduced.
- the salty seawater causes the silty particles to aggregate/accumulate into larger particles (flocculation).
- as these deposits are heavier, they are deposited first at the river's mouth.
- the main river channel will be silted and blocked up.
- river overflows and splits into many small channels called distributaries.
- as layers upon layers of alluvial materials are deposited, a platform of alluvium is built up and rises above the water.
- this flat alluvium is called a delta.

Meanders

Centrifugal force pushes water to outside of the bend.
Low energy in the river.
Undercutting followed by bank collapse. - lateral erosion and bank movement.
River cliff steep sided.
Erosion = abrasion: like sand paper against side of a bank.

Waterfalls

Class notes

Waterfall info:

how rapids are formed in the upper course

As the river moves through the upper course it cuts downwards. The gradient here is steep and the river channel is narrow. Vertical erosion in this highland part of the river helps to create steep-sided V-shaped valleys, interlocking spurs, rapids, waterfalls and gorges.

Interlocking spurs on a tributary of the Yangtse
As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs, which look a bit like the interlocking parts of a zip.
When a river runs over alternating layers of hard and soft rock, rapids and waterfalls may form.

Class notes

Deposition:
Is the laying down of material carried by the river. This occurs when there is a decrease in the energy of the river, as a result of decreased velocity and/or volume. Situations where deposition is likely as a result of decreased velocity and/or volume.

Upper:
Source: can be anything: lake, bog, melting snow etc.
Stream running through to create the v shape mountain by using vertical erosion, it’s a narrow channel – wearing a groove into the ground

Different Water transporting

Class notes

Attrition – where material is moved along the bed of a river, collides with other material and breaks up into smaller, rounded pieces.

Corrasion – fine material rubs against the riverbank and bed. A sort of sandpapering action called abrasion wears the bank and bed away.

Corrosion – some rocks forming the banks and bed of a river are dissolved by acids in the water e.g. limestone. The rocks are then eroded.

Hydraulic action – the sheer force of turbulent water hitting the banks of the river can cause joints to be enlarged or loose fragments of rock to be swept away.

Transportation by Rivers:

• Traction – where large rocks and boulders roll or slide along the riverbed.
• Saltation – where smaller stones are bounced along the riverbed in a leap frogging motion.
• Suspension – where very small grains of sand or silt are carried along with the water.
• Solution – where some material is dissolved (like sugar in a cup of tea) and is carried downstream.

Page 5a - Weathering (found in River Processes booklet)

1.
a) Freeze-thaw weathering
b) Its mean annual rainfall is around 1100 mm and its mean annual temperature is around -11
c) Chemical weathering
d) Chemical weathering

2.
a) Freeze-thaw weathering is a type of weathering that effects the planets structure for example big rocks that have small cracks collect water in-between, freeze-thaw weathering freezes the water between and brakes the rocks apart.
b) Below freezing environments
c) because there is barely any water and the mean annual temperature does not reach freezing point or below.
d) A layer of rocky particles called Regolith.

3.
a) Chemical weathering is a type of weathering that changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions.
b) A full of rain yet hot environment.
c) Because there is no water to react with the minerals and because its not hot enough to react anyway.
d) Images below in order: Limestone, Granite and chalk

Notes on weathering

Speed of weathering: depends upon the structure and mineral composition of the rocks, climate, vegetation, human influences and the time over which the weathering process operates.
The end product is a layer of rocky particles called Regolith.

Different types of Weathering

Freeze thaw:
Where does it occur?
In mountainous regions like the Alps or Snowdonia.

How does it occur?
Rainwater or snow-melt collects in cracks in the rocks.

At night the temperatures drops and the water freezes and expands.

The increases in volume of the ice exerts pressure on the cracks in the rock, causing them to split further open.

During the day the ice melts and the water seeps deeper into the cracks.

At night the water freezes again….etc.

Onion skin:
rock is repeatedly subjected to heat and cold
outer layer expands in heat
outer layer contracts in cold
outer layer of rock peels off (loose rock known as scree)

Biological:
Animals and plants can wear away rocks. This is called biological weathering. For example, burrowing animals such as rabbits can burrow into a crack in a rock, making it bigger and splitting the rock.

You may have seen weeds growing through cracks in the pavement. If you have gone for a walk in the countryside, you may even have seen bushes or trees growing from cracks in rocks or disused buildings. This is because plant roots can grow in cracks. As they grow bigger, the roots push open the cracks and make them wider and deeper. Eventually pieces of rock may fall away.

People can even cause biological weathering just by walking. Over time, paths in the countryside become damaged because of all the boots and shoes wearing them away.

Chemical:
Chemical weathering changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions. Chemical weathering is a gradual and ongoing process as the mineralogy of the rock adjusts to the near surface environment. New or secondary minerals develop from the original minerals of the rock. In this the processes of oxidation and hydrolysis are most important.
The process of mountain block uplift is important in exposing new rock strata to the atmosphere and moisture, enabling important chemical weathering to occur; significant release occurs of Ca++ and other minerals into surface waters.

Earthquakes causing TSUNAMI's

Kobe

On Tuesday, January 17th 1995, at 5.46 a.m. (local time), an earthquake of magnitude 7.2 on the Richter Scale struck the Kobe region of south-central Japan. This region is the second most populated and industrialized area after Tokyo, with a total population of about 10 million people. The ground shook for only about 20 seconds but in that short time, over 5,000 people died, over 300,000 people became homeless and damage worth an estimated £100 billion was caused to roads, houses, factories and infrastructure (gas, electric, water, sewerage, phone cables, etc).

Why did the earthquake happen here?
Three crustal plates meet near to the coast of Japan. Close to Kobe, the denser oceanic Philippines Plate is being subducted beneath the lighter continental Eurasian Plate at a rate of about 10 centimetres per year. The Japanese island arc has been formed from the molten magma released by the melting Philippines Plate. Earthquakes are very common here and happen because of the friction resulting from the two plates colliding along this destructive margin. [In 1923, the Great Kanto Earthquake killed 140,000 people in this area.] The great destruction which resulted from the 1995 Kobe Earthquake was due to the shallow depth of the focus which was only about 16 kms. below the surface and the fact that the epicentre occurred close to a very heavily populated area. Seismic shockwaves travelled from Awaji Island (the epicentre) along the Nojima Fault to the cities of Kobe and Osaka.




The Effects of the Earthquake:
The immediate effects of the earthquake are known as primary effects. They include the collapse of buildings, bridges and roads resulting from the seismic waves shaking the crust. During the 20 second earthquake, the ground moved up to 50 centimetres horizontally and up to 1 metre vertically. Some of the deaths were caused by these primary effects.
The secondary effects include the fires that broke out all over the city of Kobe, the congestion and chaos on the roads, the closure of businesses and the problem of homelessness. Many more people died in the fires that followed the earthquake. Problems were made worse by the large number of aftershocks (over 1,300).

Many of the older, wooden houses completely collapsed. Fire, triggered by broken gas pipes and sparks from severed electrical cables, caused a huge amount of damage, destroying at least 7,500 wooden homes. Office blocks built in the 1960's of steel and concrete frequently collapsed in the middle so that a whole floor was crushed but the rooms above and below remained intact. Modern buildings, designed to be earthquake proof, did quite well on the whole and suffered little damage, although some were left standing at an angle when the ground beneath them liquefied. An additional problem for rebuilding was that most people were not covered by insurance due to the difficulties of insuring such an earthquake prone area.





Almost 300,000 people were made homeless by the earthquake and had to be given emergency shelter. The severe winter weather (-2°C.) made this a serious problem. People were put into schools, town halls, open parks, etc. and were forced to live, in some cases for long periods, in overcrowded, unsanitary conditions. Food, blankets, medical supplies and clean water were, for the first few days, in short supply. The scale of the problem made it difficult for the authorities to cope.

Kobe is an important route centre. It has motorway (Hanshin Expressway) and intercity ('bullet train') railway lines passing through it and a large modern port which handles millions of tonnes of trade each year. The earthquake caused massive damage to all the transport facilities. Several sections of motorway, many of which were built above the ground on tall concrete stilts, collapsed or toppled sideways. This resulted in the Hanshin Expressway being completely closed. Railway lines were buckled and many stations damaged. A 130 kilometre section of the 'bullet train' rail network had to be closed. At the port, cranes tilted or fell and 120 (out of 150) quays where ships were moored were destroyed. Port buildings and their contents were badly damaged in many places.
Between 3% and 5% of Japan’s industry is located in and around Kobe. This includes most types of industry - from light manufacturing to high-technology and heavy industry. Due to the shortage of suitable flat land, as elsewhere in Japan, much of the industry is concentrated near the port on reclaimed land. Strong ground movements led to settlement and liquefaction in these areas and so damage to industry was severe. The difficulties of transporting raw materials and finished goods to, from, and within the region also caused great problems for well-known industries such as Panasonic and Mitsubishi. Industries affected include shipbuilding, steelworks, breweries, pharmaceutical, computer hardware and consumer goods firms.
How did the authorities cope with the earthquake?
Japan prides itself on being well prepared for earthquakes. Most new buildings and roads have, in the last 20 years, been designed to be earthquake proof, schools and factories have regular earthquake drills, etc. As it turned out, however, things did not go according to plan. Many older buildings still collapsed or caught fire. This led to many blocked roads and massive problems of homelessness. Telephones and other communication services were put out of action making communication slow and difficult. Electricity and water supplies were badly damaged over large areas. This meant no power for heating, lights, cooking, etc. Clean, fresh water was in short supply until April 1995. The government and city authorities were criticised for being slow to rescue people and for refusing offers of help from other countries. Many people had to sleep in cars or tents in cold winter conditions. A large number of the people affected were elderly and many of the effects are unquantifiable - disrupted schooling, increased unemployment, worry, stress and mental fatigue. Putting things right after the earthquake
• water, electricity, gas, telephone services were fully working by July 1995
• The railways were back in service by August 1995
• A year after the earthquake, 80% of the port was working but the Hanshin Expressway was still closed.
• By January 1999, 134,000 housing units had been constructed but some people were still having to live in temporary accommodation.
• New laws were passed to make buildings and transport structures even more earthquake proof.
• More instruments were installed in the area to monitor earthquake movements.
Copyright ©2002 Beagle Graphics (GeoResources) All rights reserved

Japan's Recent Earthquake

Factors of Damage levels during Earthquakes

Before and After responses

Primary and Secondary effects of earthquakes

Earthquakes, Richter scale's, Seismograph's and Mercalli Scale

http://en.wikipedia.org/wiki/Earthquake
http://en.wikipedia.org/wiki/Seismometer
http://en.wikipedia.org/wiki/Richter_magnitude_scale

http://science.howstuffworks.com/nature/natural-disasters/earthquake.htm
http://news.bbc.co.uk/2/hi/4126809.stm

mercalli:
http://en.wikipedia.org/wiki/Mercalli_intensity_scale

Mount Merapi - 'Mountain of Fire'

At least 64 people have been killed in the latest eruption of Indonesia's Mount Merapi volcano - more than doubling the death toll since it became active again last week.

Dozens are being treated for burns and respiratory problems after a gas cloud hit villages with even greater force than the previous eruptions.

More than 100 people are now said to have been killed.

An estimated 75,000 residents have been evacuated from the area.

Mount Merapi, one of the world's most active volcanoes, is located in a densely populated area in central Java.

The latest eruption began late on Thursday, sending residents streaming down the mountain with ash-covered faces.

Continue reading the main story
“
Start Quote

We're totally overwhelmed here”

Heru Nugroho
Hospital spokesman
Rescue workers said villages in the area were in flames.

Indonesia contains more active volcanoes than any other country on Earth. Of the 130 active volcanoes in Indonesia, Mount Merapi on the Island of Java is the most active. In fact, so active that annual offerings are made by the Javanese people to this volcano to placate its restless spirit. This conical stratovolcano's name, Merapi, is very appropriate as it means "Mountain of Fire". Typically Mount Merapi becomes active every two to three years, but large eruptions occur only every 10-15 years. In the past 500 years 68 large eruptions have been recorded. The most notable of these eruptions were in 1006, 1786, 1822 and 1872 when many people died. The lava flows, once basaltic, have in historical times become andesitic.

The present danger is increased because Mount Merapi is close to the city of Yogyakarta, a city of 0.5 milion people, and also thousands of people live almost on top ofthe volcano in villages as high up as 1700 m. A large eruption can therefore have devastating effects. In 1930 the eruption destroyed 13 villages and killed 1400 people in pyroclastic flows.

Volcanic Hazards

Tephra - solid and molten rock blasted into air
Lava Bombs
Ash
Fumeroles/ poisonous gas - sulphur dioxide
Landslides

Different eruptions

Types of Lava

A'a:
Very vicious - flows short distances
slow flowing high basaltic content
cools to a rough surface thats hard to walk on as its sharp and spiky

PaHoeHoe:
Thinner less vicious fast flowing
congeals to form thin crust thats smooth
erupts 1200 - 1200'c

Pillow Lava:
Formed in underwater volcanic eruptions cools to form hard shell
Breaks off tof orm pillow shaped blocks

- Shape of volcano depends on type of lava
- Lava type depends on its mineral content especially the silica content

Drawn Volcano

Different plates

Destructive:
80% of all volcanic activity happens on destructive margins.
Fold mountains:

Constructive: - volcanoes + earthquake
Oceanic crust moves together which makes sea floor spread/ ridges: mid Atlantic ridge: which makes Europe and America to move away from each other

Continental collision: - volcanoes + earthquake
is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of sub duction, whereby the sub duction zone is destroyed, mountains produced, and two continents sutured together.
E.g.: Andes, Himalayas

Transform/ conservative:
Fault line
Move same direction, at different speeds
Or in alternate directions

Global Distribution of Volcanoes and Hurricanes

Where are volcanoes found?

Different type of volcano's

Dome Volcano:
In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. The geochemistry of lava domes can vary from basalt to rhyolite although most preserved domes tend to have high silica content.
Lava domes are dynamic structures that evolve over time undergoing various processes such as growth, collapse, solidification and erosion.

Shield Volcano:
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes. This results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.
Shield volcanoes are built up by effusive eruptions, which flow out in all directions to create a shield like that of a warrior.

Cone Volcano:
A cinder cone or scoria cone is a steep conical hill of volcanic fragments that accumulate around and downwind from a volcanic vent.
Many cinder cones have a bowl-shaped crater at the summit. Lava flows are usually erupted by cinder cones, either through a breach on one side of the crater or from a vent located on a flank.
Cinder cones are commonly found on the flanks of shield volcanoes.

Composite Volcano:
Composite volcanoes, also called strato volcanoes, are formed by alternating layers of lava and rock fragments. This is the reason they are called composite.
Between eruptions they are often so quiet they seem extinct. To witness the start of a great eruption requires luck or very careful surveillance.
Composite volcanoes usually erupt in an explosive way. This is usually caused by viscous magma. When very viscous magma rises to the surface, it usually clogs the craterpipe, and gas in the craterpipe gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.