Lecture 11 Flashcards
What are the two main types of floods, and how do they differ?
Slow-onset (seasonal) floods develop over days to weeks due to prolonged rainfall or snowmelt, inundating large areas for extended periods. Flash floods arise suddenly from intense local rainfall or dam/levee failures, producing high-velocity, debris-laden flows.
Why are major floods less frequent than smaller floods, but often more catastrophic?
Major floods (e.g., 100-year or 500-year events) require extremely high discharge and happen infrequently, but when they do occur, they can overwhelm flood-control measures and cause widespread, catastrophic damage.
What measures are commonly used for flood control, and what risks do they carry?
Artificial levees/floodwalls and dams are common. Levees can be overtopped or breached, leading to severe flooding, and dam failures can release sudden surges of water. Even well-built structures can fail in extreme conditions.
How do we evaluate flood hazard using recurrence intervals?
A recurrence interval estimates the average time between floods of a given size (e.g., a 100-year flood has a 1% chance per year). Flood-hazard maps combine these data with local topography and hydrology to identify high-risk zones.
What is metamorphism, and how does it relate to the rock cycle?
Metamorphism is a solid-state transformation of a protolith (igneous or sedimentary) caused by changes in temperature, pressure, and chemical environment. It links igneous/sedimentary rocks to metamorphic rocks without melting.
What are the main characteristics of metamorphic rocks?
1) They contain new metamorphic minerals (e.g., garnet, kyanite). 2) They often display metamorphic textures like foliation. 3) They may appear very different from their protolith due to mineral and textural changes.
Which processes drive changes in a protolith during metamorphism?
1) Recrystallization (grain size/shape changes). 2) Phase change (new polymorphs). 3) Neocrystallization (growth of new minerals). 4) Pressure solution (dissolution/re-precipitation under stress). 5) Plastic deformation (minerals deform without fracturing).
What are the primary agents of metamorphism?
1) Temperature (heat). 2) Pressure (increased with burial/tectonics). 3) Differential stress (unequal squeezing/stretching). 4) Hydrothermal fluids (promote mineral reactions and metasomatism).
How does mineral stability affect metamorphic transformations?
Each mineral has a specific stability range under certain temperature/pressure. Clay, for example, breaks down to form new minerals at higher temperatures, whereas quartz remains stable over a wide range.
How is the ‘cooking analogy’ relevant to metamorphism?
Like cooking, metamorphism changes a rock’s ‘ingredients’ (minerals) under heat and pressure without fully melting. If conditions become too extreme, partial melting can occur (overcooking), producing migmatite.
