Deltas:)

DELTAS:
Deltas are the result of interacting fluvial (river) and, usually, marine systems.  However, they can form anywhere a stream flows into the sea.

The different types of Deltas...
1.  Arcuate (a fan-shaped delta) - e.g., Nile River.  Has many active, short distributaries taking sediment to their mouths.  The receiving (ambient) waters are rather shallow and have relatively even wave action arriving perpendicular to the shore with minimal longshore current.  As the sediment exits the many distributary mouths, the waves push it back, so the coastline is rather smooth.

2. Bird-foot (shaped like a bird foot) delta - e.g., Mississippi River.  Tend to have one or a very few major distributaries near their mouths.  The receiving basin has currents that carry the sediment away as it exits the distributary mouth.  There is a broad, shallow shelf that deepens abruptly, so the trend is to grow long and thin like a bird's toe.

3.  Cuspate (a tooth-shaped) delta - e.g., Tiber River of Italy.  Usually has one distributary emptying into a flat coastline with wave action hitting it head-on.  This tends to push the sediment back on both sides of the mouth, with a "tooth" growing out onto the shelf.

4.  Estuarine delta - e.g., Seine River of France.  This type of delta has a river that empties into a long, narrow estuary that eventually becomes filled with sediment (inside the coastline).

hope this will answer the question that miss jay gave us on monday:D

corinne and alison:D

Volcanoes

  We learnt that a volcano eruption is a release of pressure. Think of a bottle of coke that has been shaken before opening, not only coke come out, but gases comes out as well. Similarly, for a volcano, not only magma is released, different gases are released too. Knowing that volcanoes release gases when it erupts, one of the gases being released is carbon dioxide, a greenhouse gas. However, is the huge amount of such gases released from a single volcanic eruption, more or equivalent to the amount of greenhouse gases caused by human activities? Based on the U.S Geological Survey,the world's volcanoes, both on land and undersea, generate about 200 million tons of carbon dioxide annually, while our automotive and industrial activities cause some 24 billion tons of carbon dioxide every year world wide. From this, we can clearly state that greenhouse gases emissions from volcanoes comprise of less than one percent of those generated by human activities today.

  Volcanoes have different parts. A few of the four main parts are the crater, pipe, vent and the magma chamber. The definitions are all in the notes. A few questions struck my mind though. How is the pipe created? Why does the pipe go up? Why is the pipe narrow? How is the vent created?

  Volcanic hotspots were also mentioned. Hot spots are fixed places within the mantle or oceanic lithosphere, where rocks melt to generate magma.  When a hot spot is situated in the oceanic lithosphere a class of volcanoes known as shield volcanoes is built. The Hawaiian hot spot, for example, has been active at least 70 million years, producing a volcanic chain (o that extends 3,750 miles (6000 km) across the northwest Pacific Ocean. Where a hot spot lies beneath a continental plate the hot spot may generate enormous volumes of lava that accumulate layer upon layer. 


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