Earth Science 11: Weathering, Erosion and Mass Wasting
________________ is the destructive process by which rocks and minerals are broken
down through exposure to atmospheric agents such as air, ________________, and
________________________. Weathering processes can be grouped into
________________ broad categories, consisting of:
Physical weathering - the fragmentation of a larger rock into smaller pieces by
mechanical processes. These processes include




abrasion (erosion of a rock due to the impact of grains carried by wind, water, or
ice)
fragmentation during downslope movement via rockfalls, landslides, etc.
_______________________ via the freeze/thaw cycle.
thermal ________________________ and contraction via heating and cooling
___________________ weathering - breakdown of rock or mineral through reactions
between rocks/minerals and atmospheric constituents such as water, oxygen, and carbon
dioxide. The most common reactions include



Solution - molecules and elements in rocks and minerals dissolve directly into
water
Oxidation and hydration - reaction between oxygen, water, and iron-bearing
minerals that helps to break down minerals
_________________________ - a complex weathering reaction that forms clays,
the primary constituent of soils.
Ice and Physical weathering
The two principal mechanisms by which ice causes rock weathering (and erosion) are via
frost wedging and ____________________________________.

Frost wedging is the process by which water that has trickled into cracks in rocks
(ranging from microscopic to large cracks) alternates between freezing and
thawing. Frozen water (ice) occupies __________________________% greater
volume than does its liquid equivalent. Water that freezes thus pushes outward on
the sides of a fracture with tremendous force. This eventually
_______________________ rocks apart.

Glaciation - Glaciers are large masses of__________________ that rest on or
adjacent to a land surface and typically move. Glacial ice forms when snow
accumulates in deep enough piles (tens of meters) to cause individual snow flakes
to re-_______________________ and form ice. Glaciers are extremely effective
weathering and __________________________ agents. A glacier is capable of
carving deep valleys into bedrock as well as scraping all loose material (soil and
weathered bedrock) off from a landscape. In alpine regions,
__________________ glaciers are important elements in both weathering and
erosion; most alpine mountain peaks have been shaped (or carved) by small
mountain glaciers.

Water
Liquid ice or water is a key __________________ mechanism. Although water cannot
carve landscapes at the same rate as glaciers, it is nonetheless very effective at abrading
rocks and minerals and transporting erosional products over long periods. The Colorado
Plateau, which has a multi-million-year-long history of tectonic uplift, offers many
superb examples of the ability of rivers to cut downward into the rising landscapes. The
erosional topographic features are frequently spectacular.
How does water erode rock? One way it accomplishes this is through dissolutionwater dissolves minerals and carries them in ____________________. Water also
physically transports rock and mineral fragments that range in size from sand grains to
____________________________.
Streams transport material down slopes in three manners. Ions that are dissolved out of
rock or minerals in contact with water become part of a stream's dissolved load - these
ions typically will not leave the water column until they precipitate out (note that
dissolution is chemical weathering). Fine particles such as clays and other very small
rock fragments are carried as part of a stream's suspended load. These particles are too
__________________________ to settle out of the water unless the water is either still or
flows very slowly. Finally, larger rock fragments, ranging in size from sand grains to
large boulders, constitute a stream's bed load. These particles roll, slide, or bounce along
the stream bottom and thus physically abrade the stream bed.
The ability of a stream to carry material is proportional to the
______________________of the water. In alpine regions, where topographic gradients
are steep and water thus flows ____________________, water is capable of transporting
rocks as large as boulders downhill. As soon as a stream slows down (which happens
when it flows off from a steep slope onto a plain or __________________ floor), it can
no longer carry much of its bed load. Rock fragments drop out of the water and are thus
deposited at the base of a steep slope. Alluvial fans are a depositional
__________________ that forms when a stream flows out of a steep and narrow
canyon onto a valley floor and drops its bed load.

Wind
The role of wind in eroding mountain ranges is less than that of water and ice. Wind can
carry _______________________ grains that abrade and thus erode rock that is exposed
at the surface.
II. Mass wasting and gravity
Mass wasting, the downhill ____________________ of soil and rock under the influence
of ______________________, encompasses a variety of physical processes by which
mountain ranges are eroded. These processes include



Creep - slow, nearly continuous downslope movement that is induced by either
freeze/thaw cycles or wet/dry cycles.
Slides - sudden downhill movement of masses of rock or sediment.
Debris flows- dense, fluid mixtures of rock, sand, mud, and water
There are other categories of mass wasting processes such as _____________________,
rock flows, rockfalls, block glides (etc...) that can be grouped together or separately with
creep, slides, and debris flows depending on which characteristics that share in common.
All of these processes share one thing in common, namely, that they are caused by the
incessant downward pull of _______________________________.
Gravity-driven mass wasting processes are a subset of larger set of processes that
transport weathered and unweathered earth materials. These processes are classified as
erosional processes, which include all processes that remove and transport weathered or
unweathered soil and rocks. Erosional processes include






Wind
Running water
Waves
Glaciers
Water flowing underground
Gravity-driven processes (mass-wasting)
Mass-wasting processes
Mass-wasting processes such as creep, landslides, and debris flows are distinguished
from each other in part by whether they occur __________________ or
___________________. Landslides are capable of transporting massive amounts of rock
and soil ______________________ for miles in very short periods (e.g. minutes). Creep
can also transport much material, but at rates of only _______________________ per
year. Both are important erosional processes. Rapid mass wasting events such as
massive landslides or debris flows are typically triggered by events that destabilize
material that resides on steep ____________________. Such events include earthquakes,
volcanic eruptions, rain or melting snow, and poorly planned landscape alterations by
humans (e.g. road cuts or developments that require the removal of material at the bases
of slopes).
There are areas of mountains that have the peaks covered with loose rock. These loose
angular rock fragments that accumulate at the base of a slope are ______ or ________.