Name: Abigail
Status: Student
Grade: 6-8
Location: WA
Country: United States
Date: March 2007
Question:
What percentage of the rock cycle can humans view
from above the earth's surface?
Replies:
Good question. Humans can see around half the rock cycle on the
surface.
We see the formation of extrusive igneous rocks at active volcanoes.
The breakdown of rock by mechanical and chemical weathering goes on
around us all the time. But, usually this goes on so slowly that we
do not really notice it.
We can see sedimentary rocks forming on land and in the oceans. Again,
this is usually very slow, but not always. Chemical sedimentary rock is
being deposited quickly enough in hot spring areas like Yellowstone
National Park for people to see year-to-year changes.
What we cannot see is formation of intrusive igneous and most metamorphic
rocks. These rocks are created underground. Intrusive igneous rock
needs to cool slowly so a think blanket of rock above it is needed.
Although there may be some places where metamorphic rock forms at the
surface, most of these rocks need hot water, higher pressures and they
form underground as well.
We can "see" the formation of intrusive rocks using seismic surveying:
molten rock reacts differently to seismic energy than solid rock.
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