Lecture 5 Notes

Lecture 5 Notes - This outcrop is a very uncommon type of...

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This outcrop is a very uncommon type of tuff. It includes not only volcanic ash (which is normal for tuff), but also many very well-rounded pebbles and cobbles. All of this is welded very strongly together. What’s the story here?
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On the surface of the Earth there was a braided-stream system. These streams carried a lot of sediment, rounding them as they travelled downstream. Below ground, magma rose to the surface. When the magma came into contact with the ground water beneath the rivers, it caused an eruption of hot steam and ash. This combined with the river rocks to form the tuff some distance away. This type of eruption is called a phreatomagmatic eruption.
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Sedimentary rock – formed by the accumulation and cementation of sediment (physical or chemical pieces of other rock). Read sections 15.1-15.4 and Chapter 7 General principles regarding the formation of sedimentary rocks 1. Rock exposed at the Earth’s surface is not stable. It is broken down, both physically and chemically, into smaller pieces (these smaller pieces are called sediments). This process is called weathering . 2. Sediments are transported by gravity from higher areas to lower areas. This is called erosion . 3. Sediments accumulate in some areas (usually a low area, like a lake or sea). They pile up. 4. Sediments get compacted as they are buried. The increased pressure and temperature causes them to cement together, forming a sedimentary rock. This is called lithification .
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Weathering and erosion destroy high areas and fill in low areas! Without water and ice on Earth’s surface, there would hardly be any erosion. Mountains and valleys would be much, much bigger than they are now.
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Weathering and erosion destroy high areas and fills in low areas! Without water and ice on Earth’s surface, there would hardly be any erosion.
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Lecture 5 Notes - This outcrop is a very uncommon type of...

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