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