Overview of the tectonic and hydrologic systems for a GE-level course in natural disasters.

1. Photo by W. W. Little
Geological Systems

2. Dynamic Systems
From Tarbuck and Lutgens
Virtually everything we see on the earth's surface is the result of the
interaction between two dynamic systems - tectonic and hydrologic.

3. Plate Tectonics
Boundary Types
transform
divergent convergent
Plate tectonics is the theory that the earth’s surface is broken into a number of
plates that move with respect to one another.

4. Tectonic System
Unknown source
• Driven by earth's internal heat (generated by the decay of radioactive
elements, friction as material moves through the earth, and residual heat related
to planetary accretion)
• Builds things up (earthquakes, volcanic activity, mountain formation)
• Primary processes include mantle convection and isostacy

5. Earth's Internal Structure
Chemical Properties Mechanical Properties
Crust
Mantle
Core
Mesosphere
Outer Core
Inner Core
Lithosphere
Asthenosphere
From Hamblin & Christiansen
Internally, the earth consists of concentric spheres that vary according
to composition and mechanical properties. The compositional and
mechanical layers don't necessarily coincide.

6. Compositional Layering
Compositional layering occurs as low-density materials rise toward the crust and
high-density materials sink into the lower mantle and core.
There are three major compositional layers, the core, mantle, and crust, that increase
in density and thickness with depth
Crust
• Thin (up to 75 km for continents and 10 km for ocean basins)
• Low density (surface materials average 3g/cm3; whereas, the earth as a whole averages 5.5g/cm3)
• Fe/Mg-deficient silicate minerals
Mantle
• Thick (2900 km)
Bulk of earth’s mass and volume
• Moderate density
• Fe/Mg-rich silicate minerals
Core
• Thick (3500 km radius)
• Very high density
• Mostly Fe
Crust
Mantle
Core
From Hamblin & Christiansen

7. Mechanical Layering
Mechanical layering occurs as compositional layers are subjected to different levels of
heat and pressure associated with depth, which affects material flow characteristics
(rigid, fluid, plastic).
There are five major mechanical layers: inner core, outer core, mesosphere,
asthenosphere, and lithosphere.
Lithosphere
• Rigid (brittle)
• Includes crust and uppermost mantle
Asthenosphere
• Plastic (flows as a solid)
• At or near melting T/P of many minerals.
• Part of the upper mantle
Mesosphere
• Rigid
• Includes most of the mantle
Outer core
• Liquid
• Rotation-and convection-induced flow might be the
cause of earth’s magnetic field.
Inner core
• Solid
Lithosphere
Mesosphere
Outer Core
Inner Core
Asthenosphere
From Hamblin & Christiansen

8. Convection
As a material is heated, it expands lowering its density. This causes the material to
rise, where it cools, contracts, increases in density, and subsequently sinks.

9. Photo by W. W. Little

10. Mantle Convection
convection
cell
convection
cell
Rocks are heated in the mantle, causing them to expand. Expansion lowers density
and weakens the rock’s structure. This allows the rock to flow and rise toward the
earth’s surface.

11. Crustal
Features
There are two major crustal components, continental masses and ocean
basins. They differ in elevation, rock type, density, chemical
composition, age, and history.

12. Continents
Mountain Belt
Shield
Stable
Platform
Continental
Shelf
• Relatively low density rocks derived from granitic sources.
• Include oldest rocks on earth (up to 4.0 Ga).
• Divided into 4 major components; shields, stable platforms,
mountain belts, and continental shelves.

13. • Typically found along continental margins.
• Linear belts of folded sedimentary layers overlying intrusive
igneous and metamorphic rocks.
• Highly deformed by horizontal and vertical forces.
• Characterized by internal zig-zag pattern
• E.g. Rockies and Appalachians
From Tarbuck and Lutgens
Folded Mountain Belts

14. • Regional surface of low relief with gentle warping
(resembles the shape of a Greco-Roman shield).
• Metamorphic and intrusive igneous rocks formed deep
within the earth and later elevated to the surface through
isostacy as overlying material was eroded.
• E.g. Canadian shield
From Hamblin & Christiansen (2001)
Shields

15. • Horizontal and slightly deformed sedimentary layers overlying
the shields.
• Little deformation or vertical movement over hundreds of
millions of years.
Can have broad domes and basins
• E.g. U.S. Midwest between the Rockies and the Appalachians.
From Hamblin & Christiansen (2001)
Stable Platforms

16. From Tarbuck and Lutgens
Continental shelf
Continental Shelves
Continental Shelves and
slopes are considered to
be parts of continents but
form transition zones with
ocean basins.
• Submerged, flat continental area
• Very low seaward gradient
• Thick sediment cover obscures complex underlying fault structures.
Continental slope
• From edge of continental shelf to sea floor.
• Steeper than shelf, but still relatively flat.
• The base of the slope is known as the continental rise.
• Include thick, fan-shaped deposits formed by submarine "avalanches."

18. Ocean Basins
• Cover 2/3 of Earth’s surface.
• Little was known before the 1960’s.
• Relatively high density rocks derived from basaltic sources.
• Most rocks less than 150 Ma.
• Major features include oceanic ridges, abyssal floors, deep-sea
trenches, and sea mounts.
From D. T. Sandwell & W. H. F. Smith, Scripps Institute of Oceanography

19. Oceanic Ridges
From Tarbuck and Lutgens
• Extend almost continuously from the Arctic basin through the Atlantic and Indian
Oceans and across the Pacific Ocean.
• Broad, fractured swells.
• Over 1400 km wide.
• Peaks as high as 3000 m.
• Central rift valleys.
• Cut by fracture systems up to 4000 km long.

20. Abyssal Floors
• Broad, relatively smooth areas flanking the ridges.
• Ave. depth of 3000 m.
• Hills up to 900 m high cover 80 - 85% of the floor and are the most
widespread landform on Earth.
• Margins of abyssal floor covered with sediment to form the plains.
From D. T. Sandwell & W. H. F. Smith, Scripps Institute of Oceanography

21. From Lamont-Doherty Earth Observatory
• Isolated volcanic peaks
• Often found in chains
• Can form islands
Seamounts

22. Trenches
From D. T. Sandwell & W. H. F. Smith, Scripps Institute of Oceanography
• Lowest areas on Earth.
• Mariana Trench is 11,000 m below sea level.
• Located adjacent to continental folded mountain belts.

23. Hydrologic System
From Okanagan University College, Department of Geography website
• Combination of atmosphere and hydrosphere.
• Driven by the Sun and modified by the earth’s rotation.
• Responsible for storms, rivers, lakes, groundwater, sand dunes, glaciers, beaches, soil formation,
oceanic currents, global circulation patterns, climatic belts, and anything thing else involving water
or air.
• Whereas, the tectonic system builds things up, the hydrologic system wears them down.
• Primary processes include weathering, erosion, sediment transport, deposition, and lithification

24. The Water Planet
Photo by NASA
Over 2/3 of earth’s
surface is covered by
water.
The hydrologic
system involves both
surface and
atmospheric
processes.

25. Surface Runoff
Photo by W. W. Little
Much of the precipitation that falls to the earth returns to the sea as
surface runoff associated with river systems.

26. Glaciers
In mountainous regions and in high latitude areas, surface runoff can
be tied up as ice, which still flows seaward, but much more slowly.

27. Temporary Impoundment
Photo by W. W. Little
Water can be temporarily impounded in lakes and reservoirs as it
makes its way back to the sea.

28. Subsurface Flow
Photo by W. W. Little
A significant amount of
precipitation seeps into
the ground and flows back
to the sea below the
earth’s surface as
groundwater.

29. Interaction Between Systems
Earth’s tectonic and hydrologic systems form a complex set of
interactions. The local balance between these interactions is responsible
for everything we see at the earth’s surface.

30. Uniqueness of the Earth
Photo by NASA

31. Uniqueness of the Earth
Photos by NASA
All bodies in the solar system are believed to have formed at the
same time (4.6 Ga) from the same materials; however, their
surface features and internal structures are significantly different
from one another. These differences appear to be controlled by
two factors, the body’s diameter and its distance from the Sun.
Diameter affects the extent to which the tectonic system develops
and how long it subsequently endures and whether or not there is
sufficient gravity to maintain an atmosphere. Distance from the
Sun determines whether or not water can exist in a liquid state.

32. Terrestrial (Inner) Planets

33. Mercury
Mercury has no atmosphere and, due to its
small size, its tectonic system ceased to
function long ago. As a result, craters,
some of which formed billions of years
ago, dominate the planets surface. There is
no integrated drainage system and large
mountain ranges are lacking.

34. Venus
Due to its proximity to the Sun, water does not exist on Venus in the
liquid or solid states, and the planet, therefore, lacks a hydrologic
system. However, Venus is much larger than Mercury, though still
smaller than the earth, and radar mapping of its surface reveals large-scale
tectonic features, including mountain ranges. Impact craters are
also scattered across the planets surface.

35. Because of active tectonic and
hydrologic systems, the earth's
surface is in a constant state of
change. Though the earth has
undoubtebly been bombarded in
its past by meteorites and
asteroids, evidence of
extraterrestrial impact is
relatively sparse, having been
subsequently erased. The earth's
dominant features are continental
land masses and ocean basins.
Continental surfaces include
well-developed mountain ranges
as well as extensive plains. The
most ubiquitous feature of land
masses is the stream channel,
which is present at all scales
from small gullies to trunk rivers
and shows a highly developed
drainage pattern.
Earth
Photo by NASA

36. Earth’s Moon
Photo by NASA
The earth's moon is a similar size and character to the planet
Mercury.

37. Mars
Mars is smaller than either the earth or Venus but much larger than Mercury. Features,
such as volcanoes and rift valleys, indicate that Mars once had an active tectonic system,
though this appears to no longer be the case as evidenced by common well-preserved
ancient impact craters. Mars does have a thin atmosphere that generates huge dust
storms. Large-scale channel networks are evidence that water once existed in a liquid
state.

38. Gaseous Giant (Outer) Planets
With the exception of Pluto (which is no longer considered to be a
planet), the outer planets (Jupiter, Saturn, Uranus, and Neptune) consist
mostly of thick atmospheres and relatively small rocky cores of which
we know little.

39. Moons of the Outer Planets
The moons of these planets have very interesting features that are
quite different from those of the inner planets due to significantly
different compositions. Some show evidence of "ice" tectonics,
and impact craters are abundant.

40. Comets/Pluto/Kuiper Belt
Comets are blocks of ice that form an elliptical orbit, mostly in the Kuiper Belt,
around the Sun. The tail is formed by solar radiation that passes the comet and
always faces away from the Sun. Pluto is thought by many to be a dead comet.

41. The Scientific Method

42. What is Science?
The Periodic Table and the Scientific
Method
In this early depiction of the developing
periodic table, there are spaces for
elements that had been predicted to exist
but had not yet been discovered.
Photographer Unknown
According to Webster's New World Dictionary (1984), science is
“systematized knowledge derived from observation, study, etc."
From this, science can be considered as knowledge that is obtained
through a deliberate method and then organized into an understandable
system.

43. “All science is based on the assumption that the
natural world behaves in a constant and
predictable manner. The overall goal of science
is to discover the underlying patterns in the
natural world and then to use this knowledge to
predict what will or will not happen, given
certain facts or circumstances (Tarbuck and
Lutgens, 2000).”

44. Uniformitarianism
Photographer unknown Photos by W. W. Little
Modern river channels Ancient river channels
Scientists make observations of an event or an object and then try to explain those
observations by organizing them into a logical system. As rock bodies can cover extensive
areas and represent vast periods of time, much of geological research cannot be done as
controlled experiments in a formal laboratory setting. In these situations, we rely on the
assumption that chemical and physical laws are constant. That is, the processes operating
today are the same as those that operated in the past. For instance, since water flows down
hill today, it must have done so in the past. Therefore, if we identify a body of rocks that
exhibit characteristics similar to those found in modern geological environments, we assume
that they must have formed in a similar manner.

45. The Method
1) Gather data (record observations).
2) Propose a hypothesis (a preliminary, untested explanation or prediction).
Often there will be more than one (multiple-working hypotheses).
3) Test the hypothesis (try to prove or disprove).
4) Interpret the test results.
5) Accept the hypothesis as is (works repeatedly), discard the hypothesis (doesn't
work at all), or, most likely, revise the hypothesis (some parts work well, others
don't).
6) Test the revised hypothesis.
7) Make additional modifications.
8) More tests
9) More modification
10) More tests
11) Etc., etc., etc.
From the Central Arizona Regional Science and Engineering Fair
At some point, if the test results demonstrate to be consistently repeatable, the hypothesis can
be elevated to the level of a theory, representing a high level of predictability. For instance,
geologists consider the earth to have formed around 4.5 G years ago based on high consistency
from numerous tests of radioactive material obtained from the earth, from the Moon, and from
meteorites.

46. Can a theory or law
change over time?
Absolutely: the origin of the universe as an example.
Old law: The Sun, Moon, and stars revolve
around the Earth.
New law: The Moon revolves around the
Earth, the Earth revolves around the Sun, the
Earth neither revolves around the stars nor the
stars around the Earth.

47. Data vs. Interpretation
This illustration contains data
showing fluctuations in
temperature and CO2 levels
over the past 400+ ka. Based
on the similarity in pattern, it has
been interpreted by most that
there is a relationship between
the two factors.
When dealing with science, it is important to distinguish between
data and interpretations.
• Data are the facts and are recorded as observations.
Answer the question "what’s there?"
• Interpretations are explanations for those observations.
Answer the question "how did it get there?"

48. Example
Observation (data/fact):
The earth’s surface is
warmer during the day than
it is during the night.
Explanation (interpretation):
The Earth is warmed during
the day by the Sun and
cools down at night because
the Sun is absent.

49. Controlled Experiments
• In controlled experiments, usually only one factor will be tested at a
time. This is called the variable.
• All other factors remain the same from experiment to experiment
and are called constants.
• A "standard" has already been tested and has a known result and is,
therefore, used as a comparison in each experiment.

50. Open vs. Closed Systems
Open System Closed (nearly) System
An open system is one in which both energy and matter cross its
boundaries. A closed system allows energy only to enter or exit.

51. Negative Feedback Systems
Negative feedback systems adjust internally to external forces.

52. Positive Feedback Systems
Positive feedback systems feed upon, and ultimately eliminate
themselves. External forces will enhance (accelerate) internal
processes.

53. System Complexity
Geological systems can be highly complex with numerous
interdependent variables, making modeling extremely difficult.