Geomorphology Exam 1

geomorphology

the study of the processes shaping the Earth’s surface and the landforms and deposits that they produce

Nicolaus Steno (Niels Stenson)

1638-1686, developed self-named “laws”: the law of superposition and the law of original horizontality. worked within a biblical paradigm but is still considered a forerunner in geomorphology.

catastrophists

those who view geomorphology as being shaped by one abrupt and unique event

diluvialists

those that view geomorphology as being primarily shaped by the biblical flood

James Hutton

1726-1797, presented a paper arguing that the Earth’s surface was shaped by slow but continuous processes that are visible today. The work gained more traction with re-release

John Playfair

1748-1819, re-released Hutton’s work after his death

uniformitarianists

those that view geomorphology as being shaped by slow processes

Charles Lyell

1797-1875, known as the father of geology, he developed Hutton’s ideas further

Louis Agassiz

1807-1873, developed a theory that large sediment deposits in Europe and the US were the result of glaciers, not a biblical flood

Relict landforms

those shaped by processes in the past that are not at work today

T.C. Chamberlin

1843-1926, developed the concept of multiple working hypotheses and named the glacial sequence present in North America

John Wesley Powell

1834-1902, introduced base level as the elevation below which a stream cannot downcut

local base level

the lowest topographic level in a region which all the surrounding stream systems are graded to

G.K. Gilbert

1843-1918, focused on inductive reasoning and multiple working hypotheses. He was the first to suggest tectonics, the first to use flume experiments, and he developed the concept of equilibrium

William Morris Davis

1850-1934, very qualitative approach to geomorphology, assumed we understood the processes at work, interested in geographic cycles

peneplain

beveled off surface at the start and end of a geographic cycle according to William Morris Davis

J. Harlen Bretz

1882-1981, suggested a catastrophic flood in eastern Washington, and was kind of right

process geomorphology

quantitative analyses to relate geomorphic processes to land forms

Luna Leopold

1915-2006, focused on explaining the physics underlying fluvial processes

Ralph A. Bagnold

1896-1990, related physics to eolian processes

Stanley Schumm

researched the relationship between precipitation and erosion, realizing that vegetation is the critical factor

how do we know about paleo-precipitation in Jordan?

soil samples indicate paleo-wetlands (soil calcium carbonate), unconformities (indicate water table drops), and paleo-mud deposits indicate flooding

isostasy

the movement of Earth’s surface up or down due to loading (ice or water) or erosion. explains the differences in relative height between continents and oceans.

isostatic compensation

idea that for every one meter of rock eroded, 80 centimeters of uplift will occur

endogenic processes

tectonics and volcanism, drive orogenies and determine first-order topography

exogenic processes

primarily erosional, driven by the Sun’s energy and the temperature gradient between the poles and the equator

how do lithology and structure influence topography?

different rock types vary in their resistance to weathering, the type of soils they produce, and the durability of weathered material. the degree to which rocks hav been tectonically fractured, sheared, or deformed influences material strength.

what effects do plants have on topography?

they can hold soil in place, influence distribution of permafrost, and impact impact infiltration and overland flows

how do animals impact topography?

they can do so through overgrazing burrowing, and soil compaction, amongst other influences.

landscape evolution

matching types of measurements and the understanding of geomorphic processes to the spatial and temporal scales over which relevant processes act

how old are most landscapes? how long does it take them to form?

depositional landforms are not typically more than 1 million years old. it typically takes millions to 10s of millions of years to form a landscape

what relationship lies at the heart of geomorphology?

process and form

equilibrium

a delicate balance between landforms and processes

thresholds

the limits of equilibrium. when they are exceeded, the system is in disequilibrium and a major response may occur (landslide, deep stream incision)

extrinsic threshold

when a system is pushed to limiting conditions by variations in external controlling factors (climate, tectonics)

intrinsic threshold

when instability and failure of a system occur even though external variables remain relatively constant

applications of geomorphology

• feeding a growing population sustainably

• ecological restoration

• planetary exploration

• natural hazard assessment, prevention, and recovery

• foundation of rational land-use planning and landscape management

geomorphic cycle

a sequence of geological and geomorphic processes that shape and reshape the Earth’s surface over a long period of time; one is driven by natural forces such as tectonic plate movement or weathering

catastrophic event

a sudden and significant geological event that results in widespread and severe changes to the Earth’s surface

active remote sensing

involves instruments sending out a pulse of energy, receiving it back, and analyzing the characteristics of the energy pulse; ex: radar

what is InSAR and what types of events is it used for?

this is a type of radar and best used to measure changes associated with events (earthquakes, floods, small eruptions) or gradual changes over decades (groundwater subsidence, significant erosion)

what is LiDAR and when is it best used?

this is a type of radar and is best for US usage

digital elevation models

maps where points on the landscape have been assigned values for their horizontal and vertical positions, created with LiDAR and SRTM data

relative elevation models

used when elevation in regards to other area topography is more important than actual elevation (floodplain surfaces and alluvial fans)

passive remote sensing

essentially photography; uses detectors to measure the amount and wavelengths of energy emitted from the surface of the Earth such as satellite imagery

what types of field tests occur in geomorphology?

sprinkling test for slope failure, grain-size analysis for sorting, marked clasts for movement

what types of lab experiments occur in geomorphology?

physical model manipulation, flume experiments, rock weathering

how do soils change over time?

they become redder and finer textured. carbonate decreases in arid areas and clay increases

how do alluvial fans change over time?

they become darker and redder

paleomagnetic dating

uses reversal records for fine drain deposits older than 780,000 years old. useful in stream overland deposits and lake deposits

amino acid racemization

useful for anything that has proteins, such as shells, wood, or bones, with an age range of 100-100,000 years old

core stone

bedrock that has been weathered in place

how old is a landscape?

not typically over 1 million years old

how long does it take a landscape to form?

millions to 10s of millions of years

luminescence dating

works for sediments that were exposed and buried that consist of a homogenous unit with no significant weathering or water saturation, useful for wild transported sediments especially, good for things 100-200 thousand years old

horton overland flow

occurs primarily in arid areas, due to lack of permeability in a soil

saturation overland flow

occurs in humid areas due to pore spaces being filled

what factors control infiltration?

• grain size

• permeability

• vegetation

• compaction

• burrowing

• slope

• intensity and duration

• saturation

• climate/seasonality

what controls groundwater flow?

permeability and porosity

carbon-14 dating

best used on wood and coal aged around 45,000 years old

K/Ar dating

used for volcanic deposits including pyroclastic flows that are between 100,000 and 10.4 billion years old

cosmogenic nuclides

capable of dating very old materials like minerals or whole rocks, can be used to determine erosion rates as well as the age of a landform; applicable to the entire quaternary period

cesium-137 dating

based on isotope produced by nuclear bomb testing, good for recent deposition and erosion as well as understanding sources of sediment

recurrence interval

the likelihood of an event, eg a 100 year flood has a 1% chance of occurring in any given year, a 50 year flood a 2% chance, etc

groundwater sapping

seepage undermines slopes and drives mass wasting

seepage erosion

occurs along contact between permeable and impermeable units, creates groundwater sapping

features of groundwater sapping valleys

• amphitheater-shaped heads

• steep canyon headwall

• spring discharging at canyon head

• stubby drainage pattern

allogenic valleys

ones that head in insoluble rocks adjacent to karstic area and then flow into karstic region and become deeply incised

blind valleys

ones that terminate at a cliff face

pocket valleys

begin where groundwater resurges, opposite of a blind one

dry valleys

one that has no water

planetary geomorphology

use of Earth analogs to classify landforms, infer surgical processes, and gain understanding of past environmental conditions on other planetary bodies

what surface processes do we believe took place on Mars?

• weathering

• soil development

• mass wasting

• fluvial processes

• groundwater processes

• eolian processes

• glacial processes

• periglacial processes

• coastal processes

what created the moon’s topography?

• mass wasting

• weathering

• impacts

what are the main differences in boundary conditions affecting geomorphic processes on other planetary bodies?

• plate tectonics

• volcanism

• hydrological processes

• distance from the sun

• meteor bombardment

• atmosphere presence