Geomorphic Processes: I. Endogenic

I. Volcanic and Tectonic Processes – Eruptions, Earthquakes, and Landforms

Geomorphology – a major subfield of geography – Study of landforms – their origin and change over time and space

Geomorphic Processes: Physical processes which create and modify landforms on the surface of the earth

Are landform changes gradual or abrupt?

These processes operate in episodic manner – with earthquakes and volcanic eruptions causing a punctuated equilibrium

Geomorphic Processes:

A. Endogenic (Endogenous) B. Exogenic (Exogenous)

Relates closely to the Rock Cycle

A. Endogenic Processes Endogenic Processes are large-scale landform building and transforming processes

– they create relief.

1. Igneous Processes

a. Volcanism: Volcanic eruptions Volcanoesb. Plutonism: Igneous intrusions

2. Tectonic Processes (Also called Diastrophism)

a. Folding: anticlines, synclines, mountainsb. Faulting: rift valleys, graben, escarpmentsc. Lateral Faulting: strike-slip faults

Earthquakes evidence of present-day tectonic activity

Igneous Processesand Volcanoes

Igneous Processes

– involving eruptions or emplacements of molten magma from the earth’s mantle (extrusive and intrusive igneous rocks)

Volcanism : It refers to the extrusion of rock matter from earth’s subsurface to the exterior, and the creation of surface terrain features – Volcanoes are mountains or hills that form in this way.

How Volcanoes are Formed

About 95% of active volcanoes occur at the plate subduction zones and at the mid-oceanic ridges. Subduction is a process of plate tectonics where one lithospheric plate is pushed below another.

The other 5% occur in areas associated with lithospheric hot spots.

Where are Volcanoes Found?

Where are Volcanoes Found?

Convergent Plate Boundaries Subduction Zones

Oceanic-oceanic island arcsAleutian, Kurile, Marianas, Tonga

Oceanic-continental active continental marginsSouth America, North America, Central America, Kamchatka

Divergent Plate Boundaries Mid-Oceanic Ridges and Rift Valleys

Continental-Continental Continental rifts East Africa, Red Sea-Gulf of Aqaba

Oceanic-Oceanic Oceanic riftsMid-oceanic ridges, spreading sea floors, volcanic islands

Iceland, Azores

Intraplate “Hotspots” or “Mantle Plumes”

Oceanic islandsHawaii, Emperor Seamount Chains – Pacific Ocean

ContinentalYellowstone, Wyoming, USA

A volcano is generally a conical shaped hill or mountain – some active, others dormant.

Built by accumulations of lava flows, and tephra (or fragmented rock material ejected by a volcanic explosion -- also called pyroclastic material, ranging in size from volcanic ash, cinder to volcanic “bombs”

Volcanic eruptions Explosive vs. Effusive, depends

mainly on temperature and chemical differences in the magma silica-rich felsic magma has greater potential for explosive eruption basalt-based mafic magma leads to more effusive eruption

http://www.youtube.com/watch?v=uZp1dNybgfc&feature=fvw

Volcanic Landforms

Volcanic activity gives rise to such topographic features as:

Lava Flows ropy pahoehoe, and blocky aa

Volcanic Islands

• related to hot spots, as in Hawaii

• related to divergent plates and seafloor spreading, as in Iceland

Volcanic Mountains (a) Shield, (b) Cinder Cone, (c) Composite Cone or Stratovolcano and (d) Plug Dome volcanoes + (e) Caldera

SHIELD VOLCANOES

Shield volcanoes are volcanic mountains built up by the eruption of fluid, basaltic lava flowing out of a central vent.

They have broad bases with very gentle slopes

The largest shield volcano on Earth is Mauna Loa in Hawaii which rises from its base on the seafloor to a height of 17 km (10.5 miles).

Amboy Crater, southeastern California

CINDER CONE VOLCANOES

A cinder cone is a steep, conical hill of volcanic fragments that accumulate around and downwind from a vent

Cinder cones range in size from tens to hundreds of meters tall.

COMPOSITE VOLCANOES or STRATOVOLCANOESStratovolcanoes are very tall, 1000s of feet, and are typical cone-shaped mountains

Produced by alternating layers of felsic and mafic magmas, hence stratas and “Stratovolcano”

Most have snow, ice and even glaciers at top because of their heights

Eruptions are mostly explosive, but often also effusive

Examples: Mt. Shasta, Mt. Hood, Mt. Rainier, Mt. Fujiyama, Mt. St. Helen

Mt. St. Helens a typical composite volcano (before and after 1980 eruption)

PLUG DOME VOLCANOESThese volcanoes produce thick pasty lava The lava cools into angular blocks after it is slowly squeezed out of the vents

Mt. Lassen, northern California

Wizard Island and Crater Lake, Oregon

CalderaThe most explosive type of volcano is the caldera. The cataclysmic explosion of these volcanoes, and subsequent subsidence, leave a huge circular depression on Earth's surface.

Lake Toba, Indonesia

Largest recognized calderaLake Toba, Indonesia

Erupted ~ 75,000 years before present (ybp)

Measures 20 miles by 60 miles

Ejected 2500 km3 of material into atmosphere

WORLD’S LARGEST CALDERA

KRAKATAU CALDERAINDONESIA

Long Valley Caldera California

Lava flows of the Mono-Inyo Craters volcanic chain in Long Valley Caldera, California

The most recent eruptions from this chain occurred about 250 and 600 years ago

Scientists have monitored geologic unrest in the Long Valley, California, area since 1980

The central part of the Long Valley Caldera had begun actively rising

Unrest in the area persists today

http://www.youtube.com/watch?v=zh9zVXUv-Fs

YELLOWSTONE CALDERA

Plutonism: Igneous intrusions, plutons, are eventually exposed at the surface, and

tend to stand higher than surrounding landscape. Stocks, Batholiths, Laccoliths, Sills, Dikes, and Volcanic Necks.

Devil’s Tower, Wyoming: Volcanic Neck

Morro Rock: Volcanic Necks in

California

Tectonic Processesand Earthquakes

Tectonic Processes– Also called Diastrophism, it relates to:

• Tectonic forces, which not only move the lithospheric plates, but also cause bending, warping, folding, tilting, and fracturing of earth’s crust at various scales. • Such deformation

(nature, orientation, inclination and arrangement) of affected rock layers is recorded in the rock structure

Rock Structure

Near Golden Gate BridgeSan Francisco, CA

• Relative to adjacent rock masses, the rock layers may also become offset, uplifted, or down-dropped

• Orientations of inclined rock layers are measured by their strike (compass direction) and dip (angle)

Three Types of Tectonic Force and associated types of structural deformation

Compressional Tectonic Forces

• Folding – anticlines, synclines – overturn-- recumbent fold

• Faulting – reverse fault -- thrust fault (overthrust)

Tensional Tectonic Forces

• Faulting -- Fault blocks and Normal faults

– Rift valleys (Rio Grande in NM and CO, East Africa, and Dead Sea)

– Escarpment (scarp) – fault scarps

Tilted fault blocks -- Death Valley, California

Graben & Horst Topography– Basin and Range Region of western U.S.

Shearing Tectonic Forces:Lateral Faulting – strike-slip fault vs. dip-slip faults– San Andreas Fault

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tectonics_landforms/faulting_p2.html

http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/tectonics_landforms/faulting_p2.html

San Andreas Fault along the Carrizo Plainin central California

Earthquakes : Evidence of present-day tectonic activity

What is an Earthquake?• A wave-like sudden vibration or trembling in the Earth – a form of wave energy that travels through the bedrock

• Happens when accumulated tectonic stress is relieved through sudden, lurching movement of crustal blocks

along a fault line The motion is caused by quick releaseof seismic waves which travels away from a sub-surface point of sudden energy release – the Focus

Epicenter is located at the earth’s surface immediately above the focus

Although most earthquakes occur along plate boundaries or fault lines, they can also be triggered by volcanic eruptions or magma beneath the surface. Earthquakes can precede or accompany volcanic eruptions.

Earthquakes shock waves or Seismic Waves travel through the body of the Earth (BODY WAVES) and along the surface (SURFACE WAVES).

Seismic Body Waves are of two types:

P-waves (Primary waves) are faster, traveling at about 5 km/s

• These high-frequency, short waves move through solids and liquids• Ground is moved forward and backward as the wave passes through

S-waves (Shear/Secondary waves) half the P-wave speed

• High-frequency, short transverse waves move only through solids• Ground is moved upward and downward as the wave passes through

Surface Seismic Waves include Love and Rayleigh waves

Love waves vibrate the ground horizontally – A kind of ‘swaying’ motion is felt at the surface

Rayleigh waves are the slowest of all seismic waves – the ground moves up and down in response to Rayleigh wave

Measuring Earthquakes Instruments are used to record the magnitude of energy

released as well as the intensity of shaking by earthquakes

Seismographic equipment measures ground motion as a function of time

Two basic methods of measuring earthquakes are:

Richter’s Magnitude Scale: quantitative, objective, 1 – 10

Mercalli’s Intensity Scale: qualitative, subjective, I - XII

Where Do Earthquakes Occur? • Most earthquakes occur in linear belts, along tectonic plate boundaries• 80% occur around the Pacific Ocean Basin (along the Pacific Ring of Fire)

Global Distribution of Magnitude 4.5+ Earthquake Activity, 1990-1995

Rupture zones along the San Andreas Fault for each of the three major earthquakes:

January 1857 Fort Tejon ▪ April 1906 San Francisco;

October 1989 Loma Prieta

NORTHRIDGE EARTHQUAKE, 1994 January 17, 1994 4:31 a.m. 6.7 on Richter Scale

Earthquake occurred on a blind thrust reverse fault (Oak Ridge Thrust Fault system) and produced the strongest ground motions ever recorded in North America

Past Earthquakes in Southern California

CONSEQUENCES OF EARTHQUAKES

Displacement on either side of faultVertical and horizontal displacement on

Earth’s surface

SeichesMovement in an enclosed body of water due

to intense shaking – Water may actually ‘slosh out’ of the bay or lagoon

LiquefactionGroundwater rises to surface and destabilizes

soils – buildings collapse

TsunamiSeismic sea wave generated by earthquake on

ocean floor

Tsunami