INTRODUCTION TO GEOMORPHOLOGY AND EARTHS INTERNAL STRUCTURE Geomorphology

INTRODUCTION TO GEOMORPHOLOGY AND EARTH’S INTERNAL STRUCTURE

Geomorphology is the science of landforms, their origin, evolution, form, and spatial distribution. The development and changes on the Earth’s surface over time. A landform is an individual element of a landscape, a mountain, a valley, etc. Topography refers to the elevation changes of the Earth’s surface over a given space or distance. The ridges, valleys, etc.

In steady-state equilibrium (top) there is little change over time, but with dynamic equilibrium (bottom) there is a large change over time.

An example of an open system wherein energy and matter can move between different systems. Radiation (solar energy) from the Sun (one system) enter the glacier system and causes change. Matter (material input) is added to the top of the glacier, while water leaves the other end. Energy also leaves via evaporation.

Uniformitarianism is the idea that how things work now is the same way they have worked since the beginning. The processes function in the same way now as in the past and into the future. A volcano operates the same now as in the past and the processes by which a river erodes the landscape is the same now as before and will be in the future.

Example of a feedback mechanism. The darker spots in the middle are melt ponds of liquid water on the ice and being darker absorb more sunlight than the lighter areas to the right. By absorbing more sunlight, they melt more, then absorb more light, then melt more, and so on, a positive feedback. The lighter area of ice reflects more sunlight thus, staying colder, which keeps the air cold, which keeps the ice cold, …. a negative feedback.

Tectonic processes (plate tectonics, volcanoes, earthquakes, etc. ) form and re-shape the Earth’s crust.

Tectonic plates are comprised of oceanic crust, continental crust or some of each. These plates may either move apart (diverge from an oceanic ridge), come together (converge at a subduction zone to form a trench) or move side-by-side.

Volcanism is one aspect of Tectonic activity.

Damage in Kobe, Japan from an earthquake, a tectonic activity.

Tectonic processes include bending rock (folding), producing the landform seen here.

The Alps in Europe are being formed by the convergent forces between two tectonic (lithospheric) plates.

The Colorado River shaping the Grand Canyon in Az, USA is an example of fluvial processes.

Various fluvial (flowing water or river) actions are illustrated in this scene. Copyright © Richard Kesel 2002

Cone and tower karst in China is the result of the weathering process of carbonation. This process also forms caves.

Škocjan Caves in Slovenia illustrate aspects of karst geomorphology.

Historic entrance to Mammoth Cave, KY (USA).

The processes of glacial geomorphology helped to shape this landscape.

This 1899 photo shows the approximately 197 -ft. -high tidewater terminus of then-retreating Reid Glacier in Glacier Bay National Park, Alaska (USA). The hillside in the foreground is covered by a few inches of snow. No trees are present on the hillside or on any other surface in the field of view. (USGS/G. K. Gilbert) This illustrates glacial geomorphology.

Sand dunes are the result of eolian (wind) processes.

Desert pavement in the Mojave Desert in CA, USA is the result of eolian processes. Copyright © Ann Dittmer 2002

In this scene the processes of coastal waves are causing both erosion and deposition to shape the landforms.

The Big Sur area in CA, USA illustrates coastal (wave) processes.

A scene along a stretch of North Carolina (USA) beach illustrates both coastal geomorphology and human-environment interaction. Copyright © Rob Brander 2002

Internal layers of the Earth based on chemical and physical properties.

Seismic waves travelling through a homogenous planet (left) and through a differentiated planet (right). Seismic waves travel like those in the right diagram indicating the interior is not composed of all the same material, is not homogeneous.

Primary (P) seismic wave movement through the Earth. P Waves can travel thru all the internal layers of the Earth but may be refracted (bent) at some layer boundaries or change speed.

Shadow zone of seismic Secondary (S) waves which do not pass through the Core.

Internal layers of the Earth as deduced from seismic wave activity. P and S waves will change speed and direction based on the type of material through which they travel.

Earth in cross-section illustrating four of the basic internal layers.

The material in the Inner Core is in a solid state and consists primarily of iron (Fe) and nickel (Ni). The Asthenosphere is primarily molten, with some solid material. It is the main source (but not the only) of magma, the molten rock or lava which erupts onto the surface. The Outer Core is in a liquid/molten state, but also consists of Fe and Ni. It also generates most (~90%) of the Earth’s magnetic field. The Lithosphere consists of two solid layers, the Uppermost mantle, and the Crust. There are two types of crustal material, Continental and Oceanic. EARTH IN CROSS SECTION The Lower Mantle is primarily solid, but with molten material also present. It consists of Fe oxides, magnesium (Mg) and silicon (Si). The Outer Mantle is a mixture of molten and solid material and consists of silicate minerals.

Consistency (solid or molten) and major composition of the internal layers of the Earth. Do not be concerned with the numbers (depths, thickness or density) of each layer. Do know between which two layers is the Gutenberg Discontinuity located (Outer Core and Lower Mantle).

Upper internal layers of the Earth. Again, do not be concerned with the numbers, but do know between which two layers the Mohorovičić Discontinuity or Moho is located (Uppermost Mantle and Crust).

Comparison of the Earth’s radius to the distance across North America.

Earth’s upper most layers and surface, illustrating the two types of crustal material, Oceanic and Continental. The difference in density between these two types of crust is crucial in understanding plate tectonics.

An illustration depicting the basic movements of tectonic plates, diverging from an oceanic ridge and converging to form a trench.

Earth’s overall topographic relief is measured from its highest elevation above mean sea level (Mt. Everest) to its lowest level below mean sea level (Mariana Trench).

Earth’s topographic regions

Continental shields of each continental mass are the remnants of the original surface of the Earth formed over 3. 5 billion years ago.

North and South America’s diversity of landforms and ages.

Earth’s overall topographic relief as measured above and below mean sea level, ~ 20 km (12. 5 mi).

Earth’s overall topographic relief as measured from mean sea level, ~ 20 km (12. 5 mi). Mt. Everest is the highest point above sea level and the Mariana Trench contains the lowest point below sea level.

Mariana Trench location (right) and tectonic formation (above).