Chapter 14: Weathering and Karst Landscapes Flashcards
What are the exogenic and endogenic processes affecting weathering and erosion?
Exogenic - rain that freezes in rock cracks and dissolves rocks, wind that transports sediments, (Physical and chemical weathering)
Endogenic:
(tectonic activity) - the uplift and deformation of the crust influences weathering and erosion rates
(Volcanic activity) - can release ash and particles into the atmosphere
Define weathering, and explain the importance of rock type and joints and fractures in rock
-Weathering is the process that breaks down rocks between earth’s surface and slightly below
-Rock type is important because different rates of weathering can occur depending on differences in resistance of rock that may be protecting less resistant rock below
-Joint is a fracture or separation in rock that occurs without a displacement of the sides; important because it increases the surface area of the rock exposed to the weathering process
Define differential weathering and explain why it is an important factor in landscape development.
-Differential weathering is different rates of weathering as a result of differences in resistance of rocks (or intensity of weathering)
- usually results in an uneven surface when more resistant material protrudes beyond softer or less resistant material
-This process is important because it’s the reason why various landforms (like valleys, cliffs, canyons, and hoodoos) are formed, which makes the main unique look of many landscapes
-weathering and erosion break down rocks, which release minerals needed for the ecosystems and soils
Explain the factors that influence weathering processes.
-Rock composition - how a rock is formed, elements, could make it resistance or not
-Rock structure - ex. jointing
-Surface and sub-surface
-climatic conditions (rain, snow, wind heat)
-Slope orientation - controls exposure to sun, wind, rain
-faces away from solar radiation, tends to be cooler, moister, and more vegetated than ones facing direct sun
-Vegetation - vegetative cover can protect rock by shielding from raindrop impact
-roots can stabilize soil, but can also break up a rock
-Time
Describe the physical weathering processes of frost action, salt-crystal growth, pressure-release
jointing, and desiccation cracking
Freeze thaw action - water infiltrates into rock’s cracks, expands as it freezes, which causes the rock too much tension and breaks it apart
Salt-crystal growth - in warm and dry climate, evaporation removes moisture from rock surface; previously dissolved salts minerals get left behind and they accumulate and grow; that growth applies force to rock, which breaks it into pieces
Exfoliation (pressure-release) - rock peels or slips off in sheets rather than breaking; creates arch and dome-shaped features, which is formed as pressure is released from overlying rock
Desiccation cracking - clay-rich rocks and sediments expand they’re wet and contract when dry
Explain the chemical weathering processes of spheroidal weathering, hydration, hydrolysis,
oxidation, carbonation, and dissolution.
Spheroidal weathering - softens and rounds sharp edges of jointed rock when water penetrates
Oxidation - metallic elements (iron, aluminum) combine w/ oxygen to form oxides; longer, softer, and more erodible compounds formed
Hydration - water gets added to structure of mineral, changing its structure so it has a larger volume, creating stress which causes rock disintegration (mineral is changing, not being broken down)
Hydrolysis - decomposition of a chemical compound by reaction w/ water (diff from hydration because mineral is being chemically broken down
-water combines with minerals to form bigger, softer and weaker compounds
Carbonation and dissolution - water vapour readily dissolves co2 in atmosphere, making acid rain which is acidic enough to dissolve soluble minerals like calcite (CaCO3 - major ingredient in sedimentary, limestone, and metamorphic)
Provide some examples of biological weathering processes.
-Tree root wedging - tree roots split rock layers; rocks get eroded
-Lichen chelation -excrete acidic organic acids which dissolve minerals and chelate (form bonds with to whisk away) metallic ions
-Burrowing - animals living underground to create burrows that weaken structures and they collapse overtime
Ex. Rabbit holes
Define karst topography and explain which weathering processes dominates its formation. What is required for this type of topography to form?
-Karst topography refers to limestone regions w/ a specific landscape of a pitted, bumpy surface topography, poor drainage, and well-developed solution channels underground
-Chemical weathering dominates its formation
-requirements to form this type of topography:
-limestone must have 80% or more calcite
-limestone has to be jointed to provide access to sub-surface
-must have air zones in between water table and ground surface
-there has to be a vegetation cover (supplies organic acids to enhance the dissolution process)
-Karst can be formed in moist and dry and cool regions
Briefly describe the most common karst landscape features in terms of their morphology and formation processes.
Sinkholes - circular depression in ground
-forms by ground water containing acid or carbonic acid which dissolves rocks , which creates subsidence and lowers the ground surface
Karst valleys - elongated depressions formed by sinkholes uniting
Disappearing stream - surface streams are seen first, but no longer visible on top as they join an underground stream network
Caves and caverns - caves are natural underground areas big enough for humans to enter; formed by dissolution
-caverns are large caves formed by chemical processes (form beneath water table)
Dripstones - formations made of mineral deposits inside caves containing dissolved material
Stalactites- grow down from ceiling from rain of calcite
Stalagmites - build up from floor from accumulation of calcite dripping from ceiling
