Science 10: Plate Boundaries, Processes, and Landforms

Comprehensive practice flashcards for Science 10 covering Earth's interior, plate tectonics mechanisms, boundary types, fault systems, volcanoes, hotspots, and measuring techniques.

What is a tectonic plate, and what layers of the Earth make up the lithosphere?

A tectonic plate is a large, rigid slab of the Earth's lithosphere. The lithosphere consists of the entire crust plus the uppermost solid, brittle portion of the mantle, and it is cool and rigid.

How do continental lithosphere and oceanic lithosphere differ in thickness, density, and rock composition?

Continental lithosphere is thicker (around $30\text{--}70\,\text{km}$), less dense, and composed mostly of granitic rock. Oceanic lithosphere is thinner (around $5\text{--}10\,\text{km}$), denser, and composed mostly of basaltic rock rich in iron and magnesium.

Where is the asthenosphere located, and how does its rock behave under high temperatures and pressures?

The asthenosphere sits directly beneath the lithosphere in the upper mantle. Under high temperatures and pressures, its solid rock behaves in a ductile or semi-solid (plastic) manner, slowly deforming and flowing over millions of years.

Why are rigid lithospheric plates able to float and glide over the asthenosphere?

Because the underlying asthenosphere is plastic and pliable, allowing the rigid lithospheric plates above to float, rest, and glide over it.

What three interrelated forces drive the motion of tectonic plates across the Earth's surface?

The three interrelated forces that drive tectonic plate motion are mantle convection, ridge push, and slab pull.

What is the mechanism of mantle convection in driving tectonic plates?

Radioactive decay and residual heat deep within Earth warm the lower mantle, causing rock to expand, become less dense, and slowly rise. Near the upper mantle, it cools, becomes denser, and sinks, forming a circular convection current that exerts drag on the base of overlying plates.

How does ridge push contribute to tectonic plate movement?

Rising magma heats and expands the crust, elevating mid-ocean ridges above the surrounding ocean floor. Gravity causes this elevated rock to slide downward and outward along the sloping ocean floor, pushing the plate away from the ridge crest.

Why is slab pull considered the strongest driving force of plate motion?

As an oceanic plate moves away from a ridge, it cools, contracts, and becomes much denser than the underlying asthenosphere. When its leading edge enters a subduction zone, gravity pulls that heavy, cold slab downward into the mantle, dragging the rest of the plate behind it.

What is the distinction between the terms subduction and slab pull?

Subduction refers to the geological process where one plate sinks beneath another, whereas slab pull is the specific gravitational force generated by that sinking slab that pulls the entire plate along.

What relative motion occurs at a divergent boundary, and why is it called a constructive margin?

At a divergent boundary, two plates move away from each other. They are called constructive margins because brand-new crust is created along the gap.

What sequence of geological changes and landforms occurs during continental-continental divergence?

Tensional forces pull a continent apart and the crust fractures and drops to form a rift valley. Over time, the valley deepens and fills with freshwater to form long lakes, eventually dropping below sea level as seawater floods in to widen into an ocean basin.

What real-world examples illustrate continental divergence and flooded rift basins?

The East African Rift Valley (with long lakes such as Lake Tanganyika and Lake Victoria) represents an active continental rift, while the Red Sea represents a rift that has already flooded with seawater.

What occurs during oceanic-oceanic divergence to form a mid-ocean ridge?

Two oceanic plates separate under water, causing a pressure drop that allows asthenosphere magma to rise into the fracture. When the hot basaltic magma contacts cold seawater, it cools and solidifies into new seafloor rock, building an underwater volcanic mountain chain.

What is the primary global example of an oceanic divergent boundary, and where does it emerge above sea level?

The Mid-Atlantic Ridge is the primary example, and it rises above sea level in Iceland.

What is seafloor spreading?

Seafloor spreading is the continuous geological process where new oceanic crust is created along mid-ocean ridges and moves outward on both sides.

How does the age of seafloor rock samples provide evidence for seafloor spreading?

Rock samples collected from the seafloor show that the youngest rocks are located along the crest of the mid-ocean ridge, while older rocks are located progressively farther away near continental edges.

How does magnetic striping (paleomagnetism) support seafloor spreading?

As magma solidifies at mid-ocean ridges, iron-bearing minerals freeze pointing in the direction of Earth's magnetic field at that time. Symmetrical, mirrored bands of normal and reversed magnetic polarity preserved on both sides prove crust forms at the center and moves outward.

Why is the Earth not expanding despite the continuous creation of new crust at mid-ocean ridges?

Earth maintains a constant volume because the amount of crust created at divergent mid-ocean ridges is balanced by the amount of crust destroyed and recycled into the mantle at convergent subduction zones.

What relative motion occurs at a convergent plate boundary, and why is it designated as a destructive margin?

At a convergent boundary, two plates move toward each other and collide. They are designated as destructive margins because lithosphere is either recycled back into the mantle or deformed under extreme compression.

What occurs during Oceanic-Continental convergence, and what major features are formed?

The denser oceanic plate subducts beneath the thicker, more buoyant continental plate. This forms a deep trench where the oceanic plate bends downward and a chain of volcanoes on land known as a continental volcanic arc.

What is flux melting, and how does it generate magma at subduction zones?

Flux melting occurs when trapped water and hydrated sediments from a descending oceanic plate are released into the hot asthenosphere, lowering the melting point of the overlying mantle rock and generating buoyant magma that ascends to feed volcanoes.

What real-world volcanic mountain chains exemplify Oceanic-Continental convergence?

The Cascade Range in the United States (Mt. St. Helens, where the Juan de Fuca Plate subducts under North America) and the Andes Mountains in South America (along the Peru-Chile Trench, where the Nazca Plate subducts under the South American Plate).

What occurs during an Oceanic-Oceanic collision, and what landforms result?

The older, colder, and denser oceanic plate subducts beneath the younger, warmer oceanic plate. Subduction generates magma that rises through overriding oceanic crust to form underwater volcanoes that eventually rise above sea level as volcanic island arcs alongside deep trenches.

What real-world island arcs and trenches formed via Oceanic-Oceanic convergence?

The Philippine Archipelago, the islands of Japan, the Aleutian Islands in Alaska, and the Mariana Trench.

What is the Mariana Trench, and which plate's subduction formed it?

The Mariana Trench is the deepest trench in the world, formed by the subduction of the Pacific Plate.

Why is there an absence of subduction when two continental landmasses collide?

Because both continental plates have low densities, neither plate is dense enough to sink into the heavy mantle.

What geological processes and landforms characterize Continental-Continental convergence?

The continental crust crumples, folds, and thickens through orogenesis (mountain building) to produce folded mountain ranges and high plateaus, accompanied by powerful shallow earthquakes without volcanic activity.

What real-world mountain ranges were produced by Continental-Continental convergence?

The Himalayas in Asia (formed by the collision of the Indian Plate with the Eurasian Plate, producing Mt. Everest) and the European Alps.

What relative motion occurs at a transform boundary, and why is it called a conservative margin?

At a transform boundary, two plates slide horizontally past one another in opposite directions along a fault. It is called a conservative margin because crust is neither created nor destroyed.

How do earthquakes originate along transform plate boundaries?

Rough rock edges lock together by friction while plates continue trying to move, causing elastic strain to build up until it exceeds rock strength. The rocks then suddenly break and slip, releasing stored energy as seismic waves.

What are two primary real-world examples of transform boundaries cited in the notes?

The San Andreas Fault in California (Pacific Plate sliding past the North American Plate) and the Philippine Fault Zone (PFZ).

What is a normal fault, and what type of stress creates it?

A normal fault is caused by tensional stress (pulling apart). The hanging wall (the block above the fault plane) drops downward relative to the footwall.

What is a reverse fault, and what type of stress creates it?

A reverse fault is caused by compressional stress (pushing together). The hanging wall moves upward relative to the footwall.

What distinguishes a thrust fault from a standard reverse fault?

A thrust fault is a low-angle reverse fault with a slope of less than $45^\circ$ where older rock is pushed up and over younger rock by strong compressional stress.

What stress produces a strike-slip fault, and how do rock blocks displace?

A strike-slip fault is caused by shear stress. Rock blocks slide horizontally past each other with minimal vertical movement.

What is the Philippine Fault Zone (PFZ), including its length and geographical trajectory?

The PFZ is a $1,200\,\text{km}$ transcurrent strike-slip fault running from northwestern Luzon down through Masbate, Leyte, and eastern Mindanao.

What fault segments constitute the Marikina Valley Fault System, and where does the active segment run?

It includes the East Valley Fault and the active West Valley Fault, which traverses parts of Bulacan, Rizal, Metro Manila, Cavite, and Laguna.

What major active fault systems in the Philippines does PHIVOLCS recognize beyond the PFZ and Marikina Valley?

PHIVOLCS also recognizes the Central Philippine Fault Zone (Visayas), Western Philippine Faults (West Philippine Sea coastal margins and offshore), and Eastern Philippine Faults (eastern trench margin).

What is the Circum-Pacific Belt (Pacific Ring of Fire), and what makes it disaster-prone?

It is a horseshoe-shaped zone encircling the Pacific Basin dominated by convergent subduction zones, which cause frequent subduction-related earthquakes and lines of active volcanoes.

What two converging subduction systems border the Philippine archipelago?

The Eurasian / Sunda Plate subducting along the western trenches (Manila, Negros, Sulu, and Cotabato Trenches) and the Philippine Sea Plate subducting along the eastern trench (Philippine Trench).

What is a hotspot, and what does intraplate volcanism mean?

A hotspot is an area of volcanism fed by a stationary column of hot, rising mantle rock called a mantle plume originating deep within Earth. Intraplate volcanism refers to volcanic activity occurring inside the interior of a plate, far from any boundary.

How does a stationary mantle plume produce a chain of volcanic islands like the Hawaiian Islands?

As a plate drifts over a stationary hotspot, magma punches through the lithosphere to build a volcano. Plate motion carries that volcano away, shutting off its magma supply, while a new volcano forms over the hotspot, creating a chain of islands.

How does PHIVOLCS classify an active volcano, and what are four Philippine examples?

An active volcano has a record of eruption within historical times (last $600\,\text{years}$) or documented eruptions within the last $10,000\,\text{years}$ based on geological analysis (e.g., Mayon, Taal, Kanlaon, Bulusan).

How does PHIVOLCS define potentially active (dormant) and inactive (extinct) volcanoes?

Potentially active volcanoes are geologically young-looking with no historical record of eruption but evidence of past activity. Inactive volcanoes are heavily weathered and eroded, with no eruptions in the last $10,000\,\text{years}$, and expected never to erupt again (e.g., Mt. Arayat in Pampanga).

Can an extinct volcano erupt again, and what did Mt. Pinatubo's 1991 eruption demonstrate?

A truly extinct volcano cannot erupt because its magma connection is permanently gone, but dormant volcanoes can reactivate if fresh magma finds a pathway; Mt. Pinatubo erupted in $1991$ after roughly $500\,\text{years}$ of dormancy.

How do underwater subduction earthquakes trigger destructive tsunamis?

A powerful earthquake causes vertical displacement of the seafloor when the overriding plate snaps upward, lifting the water column above it. This sudden displacement sets off high-velocity waves that grow into destructive tsunamis in shallow coastal areas.

How fast do tectonic plates move across the Earth's surface?

Tectonic plates move slowly at typically $1\text{ to }10\,\text{cm/year}$, which is about the speed fingernails grow.

How do scientists use Space Geodetic Techniques (GPS/GNSS, InSAR, and VLBI) to measure plate movements?

GPS/GNSS tracks ground drift daily via satellite receivers down to the millimeter; InSAR bounces radar waves across repeated satellite passes to create deformation maps of swelling or subsidence; and VLBI tracks radio signals from quasars using radio telescopes to measure intercontinental distances.

What would happen to Earth's mountains and climate if tectonic plates permanently stopped moving?

Without compressive uplift, weathering and erosion would wear all mountains down to flat plains over hundreds of millions of years. Furthermore, the carbon cycle would fail without volcanic $CO_2$ emission and subduction recycling, causing atmospheric carbon depletion and drastic planetary cooling.

What relative motions, geological margins, and key landforms are synthesized in the lecture's Summary Review Table for the five plate boundary types?

The table outlines Divergent (Moving Apart, Constructive, forming Rift Valleys, Lakes, Oceans, Mid-Ocean Ridges); Convergent Oceanic-Continental (Colliding, Destructive, forming Deep Trenches, Continental Volcanic Arcs); Convergent Oceanic-Oceanic (Colliding, Destructive, forming Deep Trenches, Volcanic Island Arcs); Convergent Continental-Continental (Colliding, Destructive/Compressional, forming Folded Mountain Ranges, High Plateaus); and Transform (Sliding Past Horizontally, Conservative, forming Fault lines, offset features, rift scarps).