EPSC 201 Lecture 16 Notes
Recap lecture 15 at the beginning...
There are two types of weather; physical and chemical. In the desert, there is predominantly
physical weathering. Chemical weathering occurs in warm, wet climates. The chemical reactions
need water and heat to occur.
The breakdown of limestone and marble requires acid. Acid can be found naturally from the
breakdown of organic material, such as pine needles. Carbon dioxide is generated from the
breakdown of limestone, which easily leaves. The
products of the breakdown are either gaseous, or
soluble in water, which makes the breakdown very
Potassium feldspar when exposed to acid breaks
down into clay and quartz, along with potassium
ion. If the structure hasn’t broken down after
weathering, there will be lots of clay and quartz
present, because that what granite breaks down
into. Quartz is resistant to weathering, and this is
why we see nice sandy beaches of quartz.
Water is a polar molecule, and helps dissolve ions
through its dipoles.
The water molecules point their negative oxygen towards positive ions, such as potassium. The
water molecules point their positive hydrogen’s to-
wards negative ions, such as chlorine. These polar
properties make it a great solvent (the universal sol-
vent). When the rock is broken down, the ions are
dissolved into the water.
As iron is oxidized, it makes sulphuric acid. The rust
on cars is actually the mineral goethite.
There are vertical and horizontal joints in the rocks.
Joints cause physical and chemical weathering, which
explains why we observe block like rocks. Pure physi-
cal weathering causes sharp joints, while chemical
weathering causes the edges to be round. A large
number of joints greatly increases the surface area,
which causes rapid weathering. The greater the sur-
face area, the more rock is exposed to the weathering,
the faster it weathers. Biotite and feldspar breakdown and yield their
ions to be washed out. Clay is also produced,
and can be washed out. The quartz is left over,
and does not break down further.
Perfect spheres can be created through chemi-
Transport and deposition of sediment depends on how broken down the material is. If the sedi-
ment is course and large, it will be deposited close to the source. If the sediment is fine grained,
it will be transported very far from the source. Ions can travel a long way, even in underground
water, because they are soluble.
As the river moves further along, its energy is less. So at a far distance, the river is only able to
carry the fine particles, but at the beginning of the transport, the river can carry everything.
There is also the effects of breakdown, that as the particles travel further, they breakdown even
more, causing them to be smaller. So the effects of breakdown, in addition to the energy of the
river, cause there to only be fine particles at the end of transport, where as at the beginning of
transport, there is a mix of particles. The grains are rounded at the end of transport, but at the
beginning they are sharp and angular.
How do we go from broken down material to rocks? Cementation. There is a large number of
grains present, for instance quartz sand. We can cement sand into sandstone. The weight of
water forces the sediment to pack together. The
warm groundwater moves in-between the spaces
of the sediment, and cools as it moves through
the cold sediment. The ions in the solution will
precipitate (solidfy out of solution) as the water
cools. The ions are only dissolved because the
water is warm. For example, SiO2 (quartz) will
precipitate out as the groundwater is cooled in-
between the sediment. This precipitated silica
joined together all the claustic sediments. Many
sediments are cemented by silica.
Calcium carbonate (CaCO3) is another important
cementing agent. It glues together the sediment,
the same way silica does. Calcium carbonate
precipates out when the ground water is alkalai
As water goes deeper in the earth, it
gets warmer. Key point – warm water brought through cold sediment forces silica to precipitate out, and
joins together the sediments
Gravel beds of rivers can be cemented together. The long axis of the rocks always point down-
stream, so the direction of the river can be determined from rocks. These rocks form one bigger
rock with fined grained material in between the rocks, called a conglomerate. If the river is
steep and flowing fast, it is a high-energy environment, and can move all sized material. Low en-
ergy rivers are flat and can only move fine-grained material. The material of the rocks can indicat-
ed how much energy was present in the environment. Sandstone, made primary of small
grained material, forms in low energy environments.
Shale is thin layers of rock formed from mud.
Another type of sediments is glacial moraines. These are extremely variable in size, and poorly
sorted. Lots of angular fragments. Once the glacier picks up the material, it is just moved along,
and not subjected to weathering.
Rivers meander more when they are lower in energy. Fast flowing rivers are straight. The posi-
tions of meanders change over time, relatively quickly (decades). There are floodplains of each
side of the river, which flood every year (spring when the snow melts). O