Earth Science 2 Flashcards
what is a thalweg?
This is the line of lowest elevation within a valley or watercourse. the most navigable channel.
What is a pools?
These are areas of deep water and greater erosion (energy build-up due to less friction)
What are riffles?
These are areas of shallow water created by deposition of coarse sediment.
What is a point bar?
A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope.
What is a river cliff?
A cut bank, also known as a river cliff or river-cut cliff, is the outside bank of a water channel (stream), which is continually undergoing erosion.
What is. slip-off slope?
A slip-off slope is a depositional landform that occurs on the inside convex bank of a meandering river.
How are terraces formed?
A terrace can be formed as a river cuts deeper into the land. A new, lower floodplain may then be established, leaving part of the former flood plain at a higher level as a terrace.
What is the principle of uniformitarianism?
Uniformitarian Principle, is the assumption that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in the past and apply everywhere in the universe.
What are the two ways geologist tell time and date events?
Relative dating and absolute dating
What is relative dating?
This is putting things in relative order (in relation to something else) e.g rock a before rock b rock b before rock c
what is absolute dating?
This is obtaining a numerical age
what is stratigraphy?
this is a branch of geology concerned with the study of rock layers and layering (strata)
What is strata?
This is a layer of sedimentary rock or soil, or igneous rock that was formed at the Earth’s surface, with internally consistent characteristics that distinguish it from other layers.
What are some subdivisions of stratigraphy?
Lithostratigraphy
Biostratigraphy
Magnetostratigraphy
isotope stratigraphy
How old is the earth?
Approximately 4.6 billion years old
What are geochronological units?
Subdivided geological time into intervals of known durations (time units)
what are chronostratigraphic units?
These refer to rocks deposited during a specific time (time-rock units)
state the geological Time scale - geochronologic
Eon- Which is made up of Era Era - which is made up of periods Period- which is made up of epochs epochs - which is made up of age age - which is made up of chron chron
state the geological Time scale - Chronostratigraphic
Rocks deposited in the according time eon - eonothem era - earthem period - system epoch - series age - stage chron - chronozone
explain the creation of the time scale
The time scale unit durations and organization are irregular but not random they dont represent a set amount of time but instead mark major geologic events in time. the scale was created based on relative dating techniques. later absolute dates were found for the major boundaries in the time scale.
Explain the naming for the Phanerozoic eon and its era
The Phanerozoic (period of visible life) eon (there are different types of eons) and its era were named after the types of fossils seen in the rocks of this age.
Explain the naming of periods
Periods were named after the localities where they were first studied or typical lithologies form this area.
Explain the naming of epochs
Epochs of the cenozoic were named based on the similarity of their fossils to modern forms
What are the importances of the stratigraphic principles?
fundamental for analysing relationship between strata as well as used to place geologic units and features in relative order.
what are Principles of stratigraphy?
Original Horizontality lateral continuity Superposition cross-cutting relationships inclusions fossil succession
What is original horizontality?
beds are originally laid down horizontally
What is lateral continuity?
Bed extend in all directions until they thin to zero or terminate at the edge of their basin
What is superposition?
In an underdisturbed section the older beds underly the younger ones.
What are way up structures?
This are structures that help to identify which way is up so that superposition can be applied
What are some way up structures?
Graded bedding current bedding ripple marking fracture cleavage amygdaloidal lavas pillow lavas geo-petal structures/ fossil spirit levels
What is graded bedding?
a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other.
Coarser sediments at the base of beds
How does ripple marks help identifying way up?
The peaks/crest of the ripples would indicate upwards while the troughs would indicate the bottom
What are cross-cutting relationship?
The geological feature that cuts through or intrudes into another unit must be younger than the unit it is cutting
what is inclusion?
Inclusions in a rock unit are older than the rock itself
What are unconformities?
These are surfaces of erosion or non deposition
Types of unconformities?
angular unconformity
nonconformity
disconformity
paraconformity
what is an angular unconformity?
This is unconformity across which there is a change in dip. there will be a bent or angled layer and then a flat layer.
What is a non-conformity?
This is an erosion surface between non-stratified and stratified rocks.
not all rocks lay so you’ll have a rock like granite that doesn’t layer and then something happened and the stratified rock will deposit on top and layers of sediments will be there.
What is a disconformity?
This is an erosion surface across which there is no change in dip.
rocks are layered in the same direction no change in pattern but still tow different types of rock
what is a paraconformity?
This is an unconformity caused by a break in deposition with no evidence for erosion.
basically sediments will be deposited in this area but for whatever reason there is a gap in time in which the sediments top being deposited but then they start again after that gap.
what laws of stratigraphy did Nicholas steno make?
Law of superposition
the principal of original horizonaility
the principle of lateral continuity
p.s he also created the laws of constant angles
What are geo-petal structures/ fossil spirit levels?
basically this is when sediment will fill up an organism like a shell or a clam and the peel/direction in which it settles will indicate the way up.
What re the three divisions that Johann Gottob Lehmann MD recognise?`
surficial deposits
stratified mountains
vein mountains
What is karst topography and how is it formed?
A landscape that is characterized by numerous caves, sinkholes, fissures, and underground streams. Karst is a topography formed from the dissolution of soluble rocks such as limestone
What are physical surface processes?
Weathering, erosion and deposition.
What is weathering?
Weathering is the breaking down of rocks, soils, and minerals through contact with the Earth’s atmosphere, water, and biological organisms.
what is erosion?
erosion is the action of surface processes like wind, water, or other natural agents that removes soil, rock, or dissolved material from one location on the Earth’s crust, and then transports it to another location.
What is deposition?
This is a geological process in which weathered material is dumped via Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy
What are the different kinds of weathering?
Physical, chemical and biological
What is Physical weathering?
This is the disintegration of rock into smaller particles by mechanical processes without any change in chemical composition of the rock
What is chemical weathering?
This is the decomposition of rock resulting from chemical alteration and dissolution.
What is biological weathering?
Biological weathering is weathering caused by plants and animals. Plants and animals release acid forming chemicals that cause weathering and also contribute to the breaking down of rocks and landforms.
what are some types of physical weathering?
Frost wedging, salt wedging, Thermal spalling, Activity of organisms (plant roots), zones of weaknesses (bedding planes, joints)
what is frost wedging?
the mechanical disintegration of rock by the pressure of water freezing in pores and along grain boundaries.
What is salt wedging?
Salt wedging happens when saltwater seeps into rocks and then evaporates on a hot sunny day. Salt crystals grow within cracks and pores in the rock, and the growth of these crystals can push grains apart, causing the rock to weaken and break.
What is thermal spalling?
this is the breaking, cracking, peeling off of rock from intense heats. The rapid changes in temperature causes uneven expansion and contraction within the rock resulting in the development of internal stresses and strains which result in cracking.
what are bedding planes?
the surface that separates each successive layer of a stratified rock from its preceding layer
What are columnar joints?
These are formed form the cooling of igneous rocks
what is a joint?
A joint is a break of natural origin in the continuity of either a layer or body of rock
How are columnar joints formed?
They are usually formed from igneous rocks (lava flow). lava cools at the surface and causes specially uniformed contractions forming hexagonal features.
what is a joint set?
A joint set is a family of parallel, evenly spaced joints that can be identified through mapping and analysis of the orientations, spacing, and physical properties.
What is joint system?
consists of two or more intersecting joint sets.
e.g one set would be only moving in a horizontal direction while the other set would be moving in only vertical direction the intersecting of these two would make. joint system
what are the effects of physical weathering?
Smaller rocks
Increase in surface area where chemical weathering can take place
What are types of chemical weathering reactions?
Oxidation, Hydration, hydrolysis, carbonation, dissolution, organic weathering and acid rain
what is oxidation?
the breakdown of rock by oxygen in the air or water, often giving iron-rich rocks a rusty-coloured weathered surface. this causing rocks to crumble more easily.
What is dissolution?
is the process where a solute dissolves in a solvent to form a solution
what is hydrolysis?
Hydrolysis takes place when acid rain reacts with rock-forming minerals such as feldspar to produce clay and salts that are removed in solution.
What is the most common weathering products?
clay
what are the most common rock forming minerals?
Feldspars
What is the hydrolysis chemical reaction process?
feldspar + carbonic acid + water= clay dissolved silica + dissolved K + dissolved bicarbonate
2KAlSi3O8 + H2O → Al2Si2O3 + 4SiO2 + 2K + 2HC03
What is a the carbonation chemical reaction process?
Carbon dioxide + water
CO2 + H2O =H2CO3 ( carbonic acid)
Where is carbonic acid formed?
in rainwater and surface groundwater
What is carbonation?
this is the dissolution of rocks via carbonic acid which is formed from the mixing of rainwater and carbon dioxide.
what are factors that affect the rate of chemical weathering?
water and precipitation, temperature, duration of exposure, organic activity, availability of Co2 and O2, parent material
What is spheroidal weathering?
is a form of chemical weathering that affects jointed bedrock and results in the formation of concentric or spherical layers of highly decayed rock.
This is usually because the corners are the first part of the rock to be weathered and eroded. leaving a spherical formation behind
what is exfoliation?
This is the peeling away of thin outer layers. this is mainly by chemical weathering through alteration and expansion of feldspars.
What does weathering produce?
Regolith, sediment (transported and deposited) and dissolved material carried on surface water and ground water.
What are factors affecting stream flow?
Gradient, channel cross section (deep and narrow vs wide and shallow), discharge, Load, roughness of channels beds and banks
How to calculate discharge of a river?
Discharge = cross sectional area x velocity