GEOL 407- Geomorphology Fall '10 1 1. Definitions- define any 8 of the following (3 pts each) A. Karst- A term derived from the type section area of the former Yugoslavia which describes a landscape created by dissolution of the underlying carbonate bedrock and characteriszed by features like sinkholes, sinking streams and caves. B. Stream order- A hierarchical ranking system of locations where water accumulates into channels within the confines of a drainage basin. Lower order (smaller) numbers represent smaller streams and depending on which system, must converge to create larger orders (bigger streams). C. Hortonian overland flow- Downslope water movement that occurs on the ground surface that is not confined in a channel which occurs when rainfall amounts exceed infiltration capacity of the substrate. D. Terra Rosa- reddish-brown soil found mantling limestone in some karst areas. Origins are uncertain but are hypothesized to be either a weathering residuum rich in clays and iron sesquioxides or due to eolian influx of dust during limestone dissolution, or some combination of both. E. Isostatic rebound- a density-driven adjustment of the earth’s crust (in relation to the underlying mantle) in association with loading of the crust by any number of factors, including water, ice, sediment, rock etc. Isostatic rebound is defined as the crust rising to maintain a proportion of the crust above some arbitrary reference point when material is removed from the crust. F. Fluvial Terrace- a former stream floodplain abandoned during a base level fall or increased discharge interval (longer time period than a single flood) that results in stream incision, establishment of a new equilibrium, and formation of a new floodplain at lower elevations. G. Bifurcation ratio- A ratio determined by counting the numbers of streams in all stream orders, and dividing the number of any given stream order by the next successive higher order; should be between 2.5 and 5 H. Wave cut platform- A submerged shallow water bench-like erosional coastal feature created by waves eroding into a relatively uplifted area. Common in emergent coastal areas with tectonic activity, they are topographically relatively smooth, frequently associated to sea cliffs, sometimes covered with a thin veneer of sediments derived from the erosion of the coast. These become wave cut terraces once sea level falls or land levels rise. I. Baseflow- That part of stream flow that is related to longer term, more consistent contributions of groundwater to the overall flow of the stream. Can be determined by using a flood hydrograph to separate groundwater flow from that related to surface water contributions -direct runoff.
Transcript
GEOL 407- Geomorphology Fall '10
1
1. Definitions- define any 8 of the following (3 pts each) A. Karst- A term derived from the type section area of the former Yugoslavia which describes a landscape created by dissolution of the underlying carbonate bedrock and characteriszed by features like sinkholes, sinking streams and caves. B. Stream order- A hierarchical ranking system of locations where water accumulates into channels within the confines of a drainage basin. Lower order (smaller) numbers represent smaller streams and depending on which system, must converge to create larger orders (bigger streams). C. Hortonian overland flow- Downslope water movement that occurs on the ground surface that is not confined in a channel which occurs when rainfall amounts exceed infiltration capacity of the substrate. D. Terra Rosa- reddish-brown soil found mantling limestone in some karst areas. Origins are uncertain but are hypothesized to be either a weathering residuum rich in clays and iron sesquioxides or due to eolian influx of dust during limestone dissolution, or some combination of both. E. Isostatic rebound- a density-driven adjustment of the earth’s crust (in relation to the underlying mantle) in association with loading of the crust by any number of factors, including water, ice, sediment, rock etc. Isostatic rebound is defined as the crust rising to maintain a proportion of the crust above some arbitrary reference point when material is removed from the crust. F. Fluvial Terrace- a former stream floodplain abandoned during a base level fall or increased discharge interval (longer time period than a single flood) that results in stream incision, establishment of a new equilibrium, and formation of a new floodplain at lower elevations. G. Bifurcation ratio- A ratio determined by counting the numbers of streams in all stream orders, and dividing the number of any given stream order by the next successive higher order; should be between 2.5 and 5 H. Wave cut platform- A submerged shallow water bench-like erosional coastal feature created by waves eroding into a relatively uplifted area. Common in emergent coastal areas with tectonic activity, they are topographically relatively smooth, frequently associated to sea cliffs, sometimes covered with a thin veneer of sediments derived from the erosion of the coast. These become wave cut terraces once sea level falls or land levels rise. I. Baseflow- That part of stream flow that is related to longer term, more consistent contributions of groundwater to the overall flow of the stream. Can be determined by using a flood hydrograph to separate groundwater flow from that related to surface water contributions -direct runoff.
GEOL 407- Geomorphology Fall '10
2
J. Blind valley- A valley found in karst terranes where a surface stream has gone underground, leaving behind a valley with no surface outlet. K. Flood hydrograph- A plot showing time vs the discharge of a stream, commonly used to illustrate the way in which flow changes during rainfall events, and the effects of modifications to the drainage basin that contributes water to the stream on discharge. L. Recurved Spit- a sandy extension of the shoreline into deeper water areas that is created by longshore drift and curved by wave refraction creating a hook shaped landform that often occurs at the mouth of embayments M. Clint (I had to include this one… : )- the solution fractures (grikes) that separate limestone surfaces into sections that are known as clints. OR the stuff that is left behind that partially fills solution enhanced fractures N. Polje- another name for a karst gulf, that is defined as a steep walled karst collapse feature, commonly associated with coalesced sinkholes. The floor of the basin is typically covered by residuum, colluvium or alluvium from springs that rise and sink within the structure. O. Drainage density-the ratio of the total length of the streams per unit area within a drainage basin P. Stream frequency- the number of streams per unit area in a drainage basin
/24
GEOL 407- Geomorphology Fall '10
3
Using the photograph below, answer the following questions (15 pts)
2. A number of geomorphic systems are responsible for the landscape in the photograph above. One system is glaciers. Identify the other 2 system responsible for the landscape’s appearance and identify (with correct terminology) as many landforms from the non glacial systems as you can. One system is the Fluvial system and the other is the Tectonic system. The fluvial and tectonic systems are interacting through the concept of base level changes and climatic controls. The tectonically driven change in base level (orogenesis-mountains) has caused the stream system to undergo incision creating terraces. Climatic controls have initiated and ended glacial activity that modified the stream valley and controls the water in the fluvial system The Fluvial landforms visible include: terraces (2), meandering stream channel pattern, meander scars, oxbow lake, valley, and floodplain. The meander belt width in this instance appears to be much less than the width of the valley, suggesting that the current stream is an underfit stream. The primary aspect of the tectonic system is the presence of mountains, tilted strata, fault scarps..
/15
GEOL 407- Geomorphology Fall '10
4
Using the photograph below, answer the following questions. (3 and 12 pts)
3. What is the large feature outlined in white? ______a tide-dominated delta____________ 4. What processes are responsible for the dominant morphology of this fluvial feature? The delta forms initially by the stream entering a low gradient area and losing the confining properties of the valley, and losing energy, as it enters the ocean. The elongated wide distributaries (that are also estuaries in at least few cases) and a subdued protuding distal edge indicate high tidal ranges and large discharges that keep the distributaries from filling in with sediments from this river system. The extent of sediment plumes suggests a high tidal range as well as high discharges and high suspended sediment loads
GEOL 407- Geomorphology Fall '10
5
5. Tell me what geological and climatic information can derived from examination of the
photograph above. Be sure to justify your statements with an explanation supported by evidence (10 pts)
The underlying geology is likely one of horizontal carbonate lithologies, given the presence of the sinkholes on this karren and the bedding visible within the walls of the depressions. The climate of the area appears to be semi-arid to arid, as indicated by the lack of vegetation and the absence of water in the depressions. The depressions are dolines (sinkholes), which exhibit a pattern that suggests there are likely cave systems underlying where the sinks are occurring. The sinks form around the locations where the cave roof structure is weakest, allowing for collapse and sinkhole formation as the rock dissolves. The sinkholes suggest that the climate of the region was at some point slightly more humid than it is at present, or that the landscape is very old. Acidic water is necessary for doline formation, so in order for the sinkholes to form, they had to have more water (hence the more humid climate hypothesis). Or the landscape is very old and had time to create the dolines -thus the old age is needed to take advantage the limited water that does fall in the region over tens of thousands to millions of years of time to from the sinkholes). Several of the dolines have
/15
GEOL 407- Geomorphology Fall '10
6
coalesced into composite features that might be Uvalas or karst gulfs (Poljes), depending on what lines the floor of the feature
GEOL 407- Geomorphology Fall '10
7
6. Identify any three fluvial landforms on the image above and describe how they formed. (15 pts) 1) Meandering stream pattern- stream seeks path of least resistance and the molecular
structure of water combined with the relatively flat landscape and adequate water supply allows the formation of the meandering pattern
2) Oxbow lake- a meander cutoff has occurred that allowed the former channel path to be sealed off from the main channel forming a lake on the floodplain
3. meander scars- former pathways of the channel are marked by ridge and swale topography. Meander scars are created as the channel migrates laterally across the valley creating new point bars as it reworks the old flooplain into a new floodplain
4) chute and bar- point bars that are inundated during flooding create little chutes through which water flows during the high discharge events.
GEOL 407- Geomorphology Fall '10
8
5) Point bar- as the flow slows down along the inside of the meander bends, coarse sediments (sand & gravel) are deposited creating a curved bar form called a point bar
6) Mid channel islands- former mid channel bar forms, these deposits of coarse grained
material typically form downstream from areas of sediment overloading to erosion of former floodplain deposits, input from tributary streams or enlargement of chutes & bars into a more permanent channel form.
/15
GEOL 407- Geomorphology Fall '10
9
7. What feature is this, and what process(es) allowed it to form in this arid climate?. (10 pts) This is an alluvial fan. It forms as steep gradient streams confined in a narrow valley empty into relative flat low gradient surfaces that are not confined by a valley. The result of the change in conditions between the mountains and the basin is a net energy loss within the stream (decrease in flow depth and/or velocity) that results in rapid sediment deposition. The pattern on the fan surface is illustrative of braided stream channel pattern due in part to the stream being overloaded by sediments. There is no evidence of mass wasting apparent on the surface, but debris flows and mudflows might have contributed to the fan. The moisture source for the stream is the mountain highlands, where moisture is more abundant than in the dry intermontane basins. That said, the fan itself could also be the result of climate change as the climate transitioned from a moist to the current arid conditions, allowing sediments to be stripped from the valley and dumped into the basin before the water supply ran dry.
GEOL 407- Geomorphology Fall '10
10
8. What is(are) the coastal feature(s) shown and what processes is(are) responsible for their formation (10 pts) Ridge and runnel nearshore sand bars being welded onto the beach. In places there is evidence of rip currents as cut throughs on the ridges. These are formed as waves push sediments being transported by longshore currents onto the beach as submerged sand bars. Meso and microtidal ranges also can play a role in maintaining the morphology observed.
/10
GEOL 407- Geomorphology Fall '10
11
9. Complete the table below using the diagrams above Drainage basin
pattern name (1pt) Geological Interpretation (2 pts)
A Dendritic
Homogeneous unconsolidated sedemints, homogeneous unfractured or unjointed crystalline rocks or horizontal sedimentary rocks in a flat lying to moderately uplifted terrain
B Parallel
Moderate to steep parallel slopes associated with folded terrain or elongated landforms like dunes
C Trellis
Folded sedimentary, igneous or metamorphics rocks, areas of parallel fractures
D Rectangular
Jointed and/or faulted terrains where the angles of intersection are near 90°
E Radial
Volcanoes, domes and other isolated topographically elevated features
F Annular
Structural domes and basins surrounded by sedimentary strata that create hogback ridges that divert flow
Contorted coarsely layered metamorphic rocks, areas with intersecting dikes, veins, migmatites and joints
/24
GEOL 407- Geomorphology Fall '10
13
10. Examine the photo below and comment on the processes and landforms involved in the creating the landscape therein. (10 pts)
Cockpit karst (also will accept tower karst, although not completely finished in terms of creating tower formation in this view) formed in humid regions where the underlying limestone has been exposed at the surface under humid & mild climatic conditions (or even more severe in terms of moisture) that the entire landscape is essentially nothing but coalescing sinkholes, blind valleys and collapse features. Factors such as bedding thickness, strata orientation, %calcite variability, precipitation, vegetation and temperature all play a role.
