#plate boundary

[eopederson]

Mörk meginlandsplötu, Reykjanesbær, ísland, 2023.

The suture between the Eurasian (right) and North American (left) tectonic plates, among other things a prime explanation of the volcanic activity in the region and in ísland more generally. The slow moving apart of the plates has created cracks in the mantle through which lava can rise to the earth's surface. The two sides of this small rift are moving apart at annual rates measurable with a meter stick! This scene is about 25 km from the area under warning of a potential volcanic eruption at Grindavik.

I never cease to be amazed that I am old enough to remember when plate tectonics was considered an unproven theory, and it was discussed with a modicum of skepticism in earth science courses when I was an undergraduate. Now plate tectonics is to earth science as evolution is to biology, something so basic that little can be understood with out reference to it.

[earthstory]

The Big Bend

This map shows the geometry of the plate boundary between North America and the Pacific Plate. These 2 plates are grinding past each other, with about 90% of the motion represented as strike-slip displacement from the Pacific Plate heading North relative to the North American Plate. The San Andreas Fault is the southern boundary between these two plates. A large strike slip fault, the San Andreas takes up about 80% of the motion between the two plates, with the rest distributed on smaller faults throughout the two plates.

Just northeast of Los Angeles, the San Andreas does something rather odd. It bends sharply to the left, before heading back to the northwest on its path towards San Francisco. This division in the fault is nicknamed the “Big Bend”, for obvious reasons as you see here.

Faults can be represented as lines on a map, but in reality they are complex structures penetrating the entire crust. At the northern tip of the Big Bend, the San Andreas intersects another strike-slip fault, the Garlock Fault, that runs out into the Mojave Desert and disappears into heavily damaged rocks in Death Valley that are described as a “mélange” zone. Motion on the Garlock Fault, combined with other deformation in the Mojave Desert, has helped set the current course of the San Andreas.

Scientists have worked hard to understand how these faults link together and how they link to the surrounding topography. Just south of the bend in the San Andreas you will find a number of mountain ranges including the San Gabriel Mountains and the San Bernardino mountains. Both of these ranges have shot upwards in the last few million years as the San Andreas system integrated.

When faults step to the side, as we see in the Big Bend, they can create either openings filled with normal faults or mountains. In this case, the rocks riding northwards along the San Andreas basically run into a brick wall – they slam into the bend in the fault, creating compressive forces as they are forced to the side. This compression is shoving up the mountain ranges that surround the Los Angeles basin and has created faults and the Tranverse Mountain Ranges to the west as material is pushed to the side.

-JBB

Image source: https://commons.wikimedia.org/…/File:Sa…

References: http://bit.ly/2zwua5j http://bit.ly/2hZEOu3 http://scedc.caltech.edu/…/sec1pg27.html

[thesilicontribesman]

Logsogumadhr

He climbs high volcanic stone to touch solstice sun;

old age measures tender warmth from fleeting rays.

For fifteen days the gathering gothar will listen,

memory mapped to landscape; a geography of law.

Tomorrow will bring the duelling of words; dispute

stitched by knotty detail and hardship; Icelandic love.

In the morning, clans will eat, wash in cold, marsh water,

exploring the infinite ways language can carve rock.

He fears the movement of tectonic boundaries, change

wrought by basalt and iron; his mind wanders now.

His apprentice gathers air, stutters, mimics justice.

History erupts; ash clouds obscure a faltering light.

Written by The Silicon Tribesman

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[didyoujustlickme-]

The exposure of the boundary between the Pacific (upper) and Australian plates, what a cataclastic mess!

The green zone between the mylonite/ultramylonite upper plate and (there were some Keas come to investigate the group of students on the mountain, idk what’s on the Australian plate I wasn’t listening whoops!) the lower is from metamorphosed glass and clay, turned chlorite.

Gaunt creek, New Zealand

[ijtsrd]

The Suture Line: Himalayan Belt

By Biplab Tripathy"The Suture Line: Himalayan Belt" 

Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-2 | Issue-4 , June 2018, 

URL: http://www.ijtsrd.com/papers/ijtsrd12905.pdf  

http://www.ijtsrd.com/humanities-and-the-arts/social-science/12905/the-suture-line-himalayan-belt/biplab-tripathy

international journals of computer science, call for paper engineering, ugc journal list

Suture is very common term used to explain the plate boundary in geography and geology. The term suture is a medical term but geographically it refers to the area of convergent plate margin. Area is very important for the study of tectonic landforms. The Himalayan belt is a great example of suiter line lies between Eurasian and Indian plate. It is longest suture in the theory of plate-tectonic. The suture is very sensitive for its destructive nature. Orogenesis process made the region very differ from other. Various natural disasters are happened on suture. Nepal earth quake is a very recent devastating phenomenon on Indo-Eurasian suture. 

[the-gneiss-blog]

Volcanic hazards

Types of volcanic eruptions and associated plate boundary

Volcanoes and eruptions can be classified under different categories

Nature of vent through which magma escapes onto the surface

Central vent

Linear fissures

Type of magma

Acidic --> viscous

Intermediate

Basic --> fluid

Type of eruption (degree of explosive violence) and nature of deposits

Hawaiian eruption --> very little explosive activity, basic lava which is very fluid and has no built-up gas 

Strombolian eruption --> mild to moderately explosive, occur regularly, basic lava but less build than lava from Hawaiian eruptions

Vulcanian eruption --> occur less frequently than Strombolian eruptions, magma is more viscous and ejected magma is thrown further, comprising solid blocks and ash

Vesuvian eruption --> plume of gas and ash is obvious as it rises upwards like a cauliflower several km into the sky

Plinian eruption -->Highly explosive, ejecting large quantities of gas and tephra which are propelled into the clouds 60km above sea-level

Peleean eruption --> infrequent eruptions but highly intense and accompanied by lateral blasts, involves highly acidic and hence viscous lava which forms a dome/plug blocking the crater in which pressure builds up, resulting in very violent eruptions

Note that these factors are in turn determine by the locations of the volcanoes and the types of plate boundaries they are associated with.

Types of volcanic features & activities at divergent/constructive boundaries:

Fissure eruptions --> flood basalt

Outpourings of large quantities of basalt

Accumulation of these outpourings over long periods of time form basalt/lava plateaus which can completely obscure pre-existing topography

Over time, extensive surfaces build up forming plateaus --> Columbian plateau in North America, Deccan Plateau in NW India and the Drakensberg Mts in Africa

Central vent eruptions --> shield vocanoes/ basic lava domes

Hawaiian eruptions

e.g. Volcanic islands of Hawaii --> they overlap 

Built up from thousands of lava flows, each of which isn’t very thick

Gentle gradient of the flanks of the volcanoes (between 2-10º)

Huge diameter --> 100km at the submerged base, making it a very large feature 

Types of volcanic features & activities at convergent/constructive boundaries:

All/most of them are associated with central vent eruptions

Volcanic cones

Cinder cones

Strombolian eruption

At most 300m tall

Steep gradient, steepest nearer the rim and gentler at the base

Presence of large central craters

Paricutin, West of Mexico City

Strato-volcanoes/composite cones

Vulcanian/Plinian eruptions

Andesitic laval, therefore rather explosive 

Comprises of interbedded eval flows and beds of pyroclasts

Reach few 1,000 in height

Steep slopes --> 20-30º

Usually symmetrical in profile by irregularities may be produced by intrusion of dykes, formation of flank fissures and parasitic cones 

May have more than 1 vent, craters and collapsed structures due to long history of eruption

Fujiyama in Japan, Vesuvius in Italy, Mt St Helens in the US

Acid lava domes

Composed of very viscous, usually rhyolitic lava

Slow moving flows solidify very quickly

Small scale features only few 100m in height

Steep sided

Eruption craters --> due to intense and explosive eruptions

Openings at the top of volcanic cones

Funnel-shaped depressions due to the accumulation of material after explosive ejection

May be enlarged and steepened by major blasts

When volcanic activity ceases, crater tends to be filled up by debris from walls as they undergo weathering & erosion

Calderas

Formed due to subsidence

Circular depressions with flat bottoms and steep walls

May be several km in diameter

Form when magma chambers of very large volcanoes empty out and leave an unsupported roof

e.g. Crater Lake in Oregon, USA

[alansgcsegeography]

Destructive plate boundary

 Destructive

At these plate boundaries the two plate are being pushed      together.

 these form at boundaries where a oceanic plate meets continental plate. the denser oceanic plate is forced beneath the lighter continental plate. this pushes the oceanic plate down into the mantle destroying it but also causing friction between the two plate this adds to the rate of plate destruction and can cause magma chambers to form which in turn creates violently erupting volcanoes.

the place where the two plates meet also forms ocean a deep ocean trench due to the oceanic plate bending under the continental plate.

[vulpezvulpez]