IASNOVA Interactive Atlas · Dynamic Earth
TECTONIC PLATES, EARTHQUAKES & VOLCANOES
52 tectonic plates · 7 boundary classes · 1,196 Holocene volcano records · 100 earthquakes of M8.0+ since 1900
Hover or tap a plate, boundary, earthquake or volcano. PB2002 · Smithsonian GVP · USGS catalog snapshot: 19 July 2026.
Earth’s surface is not one unbroken shell. It is divided into moving lithospheric plates whose interactions build mountains, open oceans, generate earthquakes and feed most of the world’s volcanoes. The map above lets you isolate each process and observe the global pattern directly.
1. Earth’s Mechanical Layers
The lithosphere consists of the crust and the rigid uppermost mantle. It is broken into plates. Beneath it lies the hotter, weaker asthenosphere, which remains solid over short timescales but can flow slowly over geological time. The deeper mantle transports heat through convection, while the metallic outer core is liquid and the inner core is solid.
Continental lithosphere
Generally thicker, more buoyant and compositionally diverse. Continental crust is commonly granitic to intermediate and can preserve rocks billions of years old.
Oceanic lithosphere
Generally thinner and denser. Basaltic oceanic crust forms at ridges, cools and thickens with age, and is commonly recycled at subduction zones.
Lithosphere versus crust
A plate is not simply a piece of crust. It includes the crust plus the rigid uppermost mantle attached to it.
Asthenosphere
A mechanically weak part of the upper mantle that can deform and flow, permitting rigid plates to move above it.
2. Why Plates Move
Plate motion results from gravity acting on density differences together with mantle flow. Slab pull occurs when cold, dense oceanic lithosphere sinks at a subduction zone and pulls the trailing plate. Ridge push is the gravitational sliding of lithosphere away from elevated spreading ridges. Basal tractions associated with mantle circulation also influence plates. The process is a coupled system rather than a single conveyor belt.
Rates are typically measured in millimetres or centimetres per year—similar to fingernail growth—but sustained motion over millions of years can open oceans and raise vast mountain systems.
3. Types of Plate Boundaries
| Boundary | Plate motion | Earthquakes | Volcanism | Typical landforms and examples |
|---|---|---|---|---|
| Divergent | Move apart | Mostly shallow; commonly normal faulting | Basaltic magma from decompression melting | Mid-ocean ridges, rift valleys; Mid-Atlantic Ridge, East African Rift |
| Transform | Slide laterally | Shallow and potentially destructive; strike-slip motion | Usually limited because crust is neither created nor deeply subducted | Linear faults and offset features; San Andreas, North Anatolian Fault |
| Ocean–continent convergence | Oceanic plate subducts | Shallow to deep along the descending slab | Continental volcanic arc | Trench and mountains; Andes and Peru–Chile Trench |
| Ocean–ocean convergence | One oceanic plate subducts | Shallow to deep; megathrust and in-slab events | Volcanic island arc | Trench and island arc; Mariana, Aleutian and Tonga systems |
| Continent–continent convergence | Crust shortens and thickens | Mostly shallow to intermediate; large thrust earthquakes | No continuous subduction volcanic arc | Fold mountains and plateaus; Himalaya–Tibet |
Real boundaries are not always narrow or simple. Oblique motion can combine convergence with strike-slip faulting, while broad orogenic belts such as the Mediterranean–Himalayan zone distribute deformation across hundreds of kilometres.
4. Earthquakes: Origin, Depth and Measurement
An earthquake begins when stress overcomes friction on a fault and rocks rupture or slip suddenly. The underground origin is the focus or hypocentre; the point directly above it is the epicentre. Energy travels as compressional P waves, shear S waves and slower surface waves. P waves pass through solids and liquids, while S waves do not travel through liquids.
Shallow-focus: 0–70 km
Found at every boundary type and responsible for most damaging shaking because rupture is close to the surface.
Intermediate: 70–300 km
Associated mainly with descending slabs in subduction zones.
Deep-focus: 300–700 km
Restricted to cold subducting slabs. No confirmed tectonic earthquakes originate much deeper than about 700 km.
Magnitude versus intensity
Magnitude quantifies event size; moment magnitude is widely used. Intensity records local shaking and damage and therefore varies by location.
The world’s largest earthquakes are generally megathrust events on subduction interfaces. A long locked boundary can store elastic strain for centuries before rupturing. Transform faults can also cause catastrophic shallow earthquakes, while divergent-boundary earthquakes are normally smaller.
5. Volcanoes and Magma Generation
Rock melts when temperature rises, pressure falls or volatiles lower its melting point. At mid-ocean ridges and continental rifts, rising mantle experiences decompression melting. At subduction zones, water-rich fluids from the descending slab trigger flux melting in the mantle wedge. Hotspots generate intraplate volcanism through localized mantle melting. The slab is not simply melted by friction.
| Volcano form | Typical magma and behaviour | Examples |
|---|---|---|
| Shield volcano | Broad, gentle slopes; usually fluid basaltic lava and mainly effusive eruptions | Mauna Loa, Kilauea |
| Stratovolcano | Steep layered cone; commonly andesitic to dacitic magma; explosive and effusive activity | Fujisan, Merapi, Cotopaxi |
| Cinder cone | Small, steep cone built from loose scoria and other pyroclasts around a vent | Parícutin and many monogenetic cones |
| Caldera system | Large depression formed when the roof collapses after substantial magma withdrawal | Toba, Santorini, Yellowstone volcanic system |
| Fissure eruption | Lava erupts along elongated cracks, sometimes producing extensive basalt fields | Icelandic fissure systems, Deccan Traps in the geological past |
Silica-rich magma is generally more viscous and traps gases more easily, increasing explosive potential. Basaltic magma is usually less viscous, but basaltic eruptions can still be dangerous through lava flows, gas, ash, fissure activity and interaction with water.
6. Global Earthquake and Volcanic Belts
Circum-Pacific Ring of Fire
A horseshoe-shaped chain of subduction zones, trenches, island arcs and continental volcanic arcs surrounding much of the Pacific. It contains a dominant concentration of global seismic and volcanic activity.
Alpide or Mediterranean–Himalayan belt
Extends from the Mediterranean through Türkiye, Iran and the Himalaya toward Southeast Asia. Continental collision, subduction and major strike-slip faults interact here.
Mid-ocean ridge system
A continuous global divergent network. Most ridge volcanism occurs underwater, and earthquakes are shallow.
East African Rift
A continental divergent system marked by normal faults, deep lakes, volcanic centres and the gradual separation of Nubian and Somali plate regions.
Hotspot chains
Hawaii, Galápagos, Réunion and other intraplate volcanic systems record plate motion over localized melting anomalies.
Diffuse deformation zones
In places such as Central Asia and the Mediterranean, deformation is spread across many faults instead of one sharply defined boundary.
7. Tsunamis and Cascading Hazards
Most major tectonic tsunamis follow large, shallow undersea earthquakes that vertically displace the seabed. Tsunami waves travel rapidly across deep oceans with low height, then slow and grow as water becomes shallow near a coast. Submarine landslides, volcanic collapse and eruptions can also generate tsunamis. Earthquake hazards further include ground shaking, surface rupture, liquefaction, landslides, fires and infrastructure failure; volcano hazards include ash fall, pyroclastic density currents, lava, lahars and gases.
8. Evidence for Plate Tectonics
Continental fit and fossils
Matching coastlines, rock belts and fossils on separated continents supported earlier continental-drift ideas.
Seafloor magnetic stripes
Symmetrical bands of normal and reversed magnetism on both sides of ridges record repeated crust formation and geomagnetic reversals.
Ocean-floor age
Crust is youngest at spreading ridges and becomes older away from them; no very ancient oceanic crust survives because it is recycled.
Global earthquake patterns
Epicentres and earthquake depths outline ridges, transforms and inclined subducting slabs.
Volcano distribution
Volcanic arcs parallel trenches, ridge volcanism follows divergence, and hotspot tracks record moving plates.
Modern geodesy
Satellite-based measurements directly record plate velocities and strain accumulation across active faults.
9. Complete Reference
Major tectonic plates
Pacific Plate
Type: Major oceanic plate
General motion: Generally northwest relative to major mantle hotspots
Key boundaries: Ring of Fire subduction zones, East Pacific Rise and major transforms
Study note: The largest tectonic plate; most of its margins are seismically and volcanically active.
North America Plate
Type: Major continental-oceanic plate
General motion: Generally west-southwest relative to Eurasia across the Atlantic
Key boundaries: Mid-Atlantic Ridge, San Andreas system, Aleutian and Cascadia subduction zones
Study note: Includes continental North America, Greenland and oceanic crust extending to the Mid-Atlantic Ridge.
South America Plate
Type: Major continental-oceanic plate
General motion: Generally westward away from the Mid-Atlantic Ridge
Key boundaries: Nazca subduction at the Peru-Chile Trench and divergence from Africa
Study note: Nazca Plate subduction uplifts the Andes and generates major earthquakes and volcanoes.
Eurasia Plate
Type: Major continental-oceanic plate
General motion: Complex motion; generally eastward in its western and central sectors
Key boundaries: Mid-Atlantic Ridge, Mediterranean convergence and Himalayan collision
Study note: Its southern margin is a broad collision zone rather than one simple boundary line.
Africa Plate
Type: Major continental-oceanic plate
General motion: Generally north-northeast
Key boundaries: Mid-Atlantic and Indian Ocean ridges, Mediterranean convergence and East African Rift
Study note: Continental rifting is gradually separating the Somali Plate from the Nubian part of Africa.
Antarctica Plate
Type: Major continental-oceanic plate
General motion: Slow motion surrounded mainly by spreading ridges
Key boundaries: Southwest, Southeast and American-Antarctic ridges
Study note: It is almost completely encircled by divergent oceanic boundaries.
Australia Plate
Type: Major continental-oceanic plate
General motion: Rapidly north to northeast
Key boundaries: Sunda collision-subduction system and Tonga-Kermadec region
Study note: Northward movement drives intense deformation from Indonesia to New Guinea and New Zealand.
India Plate
Type: Major continental plate
General motion: North-northeast toward Eurasia
Key boundaries: Himalayan continental collision and Indian Ocean ridges
Study note: India’s continuing collision with Eurasia raises the Himalaya and causes powerful earthquakes.
Arabia Plate
Type: Major continental plate
General motion: North-northeast away from Africa
Key boundaries: Red Sea and Gulf of Aden rifts; Zagros collision
Study note: New oceanic crust forms along the Red Sea while Arabia collides with Eurasia in the Zagros.
Nazca Plate
Type: Major oceanic plate
General motion: Eastward toward South America
Key boundaries: East Pacific Rise and Peru-Chile subduction zone
Study note: Its subduction beneath South America produces the Andes volcanic arc and megathrust earthquakes.
Cocos Plate
Type: Oceanic plate
General motion: Northeast toward Central America
Key boundaries: East Pacific Rise and Middle America Trench
Study note: Subduction beneath Central America feeds a chain of active volcanoes from Mexico to Costa Rica.
Caribbean Plate
Type: Regional oceanic-continental plate
General motion: Generally eastward relative to the Americas
Key boundaries: Lesser Antilles subduction and northern-southern transform systems
Study note: Its mixed boundary types explain the region’s earthquakes, volcanic islands and deep trenches.
Philippine Sea Plate
Type: Oceanic plate
General motion: Generally northwest
Key boundaries: Izu-Bonin-Mariana and Philippine-Ryukyu subduction systems
Study note: It lies between opposing subduction systems in one of Earth’s most complex tectonic regions.
Juan de Fuca Plate
Type: Small oceanic plate
General motion: East-northeast toward North America
Key boundaries: Juan de Fuca Ridge and Cascadia Subduction Zone
Study note: It is a remnant of the ancient Farallon Plate and subducts beneath the Pacific Northwest.
Scotia Plate
Type: Small oceanic plate
General motion: Generally eastward between South America and Antarctica
Key boundaries: Transform margins and South Sandwich subduction zone
Study note: Its motion helps shape the curved Scotia Arc between southern South America and Antarctica.
Somalia Plate
Type: Regional continental-oceanic plate
General motion: East-southeast relative to the Nubian Plate
Key boundaries: East African Rift and Indian Ocean spreading ridges
Study note: Continental rifting along East Africa may eventually create a new ocean basin.
Sunda Plate
Type: Regional plate
General motion: Complex motion at the southeast edge of Eurasia
Key boundaries: Sunda Trench and Indonesian collision zones
Study note: Subduction of Indo-Australian oceanic lithosphere produces Indonesia’s volcanoes and megathrust earthquakes.
Anatolia Plate
Type: Regional continental plate
General motion: Westward relative to Eurasia
Key boundaries: North and East Anatolian fault systems
Study note: It is squeezed westward by Arabia-Eurasia convergence and bounded by destructive strike-slip faults.
Important plate-boundary zones
Mid-Atlantic Ridge
Boundary type: Divergent boundary
Plates: North American–Eurasian and South American–African plates
Importance: A slow-spreading ocean ridge that rises above sea level in Iceland. It creates new Atlantic ocean floor and produces shallow earthquakes and basaltic volcanism.
East Pacific Rise
Boundary type: Divergent boundary
Plates: Pacific–Nazca and Pacific–Cocos plates
Importance: A fast-spreading ridge. Its broad elevation, abundant hydrothermal activity and lack of a deep central rift contrast with many slow-spreading ridges.
Red Sea and Gulf of Aden
Boundary type: Divergent boundary
Plates: Arabia–Africa–Somalia plates
Importance: Continental rifting has progressed to young seafloor spreading. The Afar region links three rift arms at a triple-junction zone.
East African Rift
Boundary type: Continental rift
Plates: Nubian–Somali plate system
Importance: Normal faulting, elongated lakes and volcanism mark an active continental rift that may eventually form a new ocean basin.
San Andreas Fault System
Boundary type: Transform boundary
Plates: Pacific–North American plates
Importance: Mostly horizontal right-lateral motion produces frequent shallow earthquakes but little magma generation.
North Anatolian Fault
Boundary type: Transform boundary
Plates: Anatolian–Eurasian plates
Importance: A major right-lateral fault accommodating the westward escape of Anatolia; it has produced a sequence of destructive earthquakes.
Alpine Fault, New Zealand
Boundary type: Oblique transform boundary
Plates: Pacific–Australian plates
Importance: Horizontal slip combines with convergence, helping uplift the Southern Alps while generating major earthquake hazard.
Peru–Chile Trench
Boundary type: Subduction zone
Plates: Nazca beneath South America
Importance: Creates the Andes volcanic arc, deepens earthquakes landward beneath the continent and produces some of the largest megathrust earthquakes.
Middle America Trench
Boundary type: Subduction zone
Plates: Cocos beneath North America and Caribbean
Importance: Feeds the Central American volcanic arc and generates shallow megathrust plus deeper in-slab earthquakes.
Cascadia Subduction Zone
Boundary type: Subduction zone
Plates: Juan de Fuca beneath North America
Importance: A locked megathrust off the Pacific Northwest; the Cascade volcanoes form on the overriding plate.
Aleutian Trench
Boundary type: Subduction zone
Plates: Pacific beneath North America
Importance: Forms the curved Aleutian island arc and a long belt of shallow-to-deep earthquakes.
Japan–Kuril–Kamchatka System
Boundary type: Subduction system
Plates: Pacific beneath Okhotsk/North American margin
Importance: A complex chain of trenches and volcanic arcs associated with frequent great earthquakes and tsunamis.
Izu–Bonin–Mariana System
Boundary type: Subduction zone
Plates: Pacific beneath Philippine Sea and Mariana plates
Importance: Includes the Mariana Trench, island-arc volcanoes and a well-developed Wadati–Benioff earthquake zone.
Sunda Trench
Boundary type: Subduction zone
Plates: Indo-Australian lithosphere beneath Sunda
Importance: Source region of Indonesian volcanic arcs and the 2004 Sumatra–Andaman megathrust earthquake and tsunami.
Tonga–Kermadec Trench
Boundary type: Subduction zone
Plates: Pacific beneath Tonga–Kermadec/Australian system
Importance: Among Earth’s most seismically active and deepest subduction systems, with rapid plate convergence.
Himalaya–Tibet Collision Zone
Boundary type: Continental convergence
Plates: India–Eurasia
Importance: Crustal shortening and thickening built the Himalaya and Tibetan Plateau. Earthquakes are powerful, but a continuous volcanic arc is absent.
Alpine–Mediterranean Belt
Boundary type: Continental convergence and subduction
Plates: Africa–Arabia–Eurasia
Importance: A broad, complex deformation belt extending from the Mediterranean through Türkiye and Iran toward the Himalaya.
Lesser Antilles Arc
Boundary type: Subduction zone
Plates: Atlantic oceanic lithosphere beneath Caribbean
Importance: Produces an island arc, deep trench, explosive volcanoes and earthquake-tsunami hazards in the eastern Caribbean.
Selected world volcanoes
Kilauea
Location: United States · Eastern Pacific Volcanic Regions
Volcano type: Shield
Last known eruption: 2026
Tectonic setting: Intraplate / Oceanic crust (< 15 km)
Reference note: Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift…
Mauna Loa
Location: United States · Eastern Pacific Volcanic Regions
Volcano type: Shield
Last known eruption: 2022
Tectonic setting: Intraplate / Oceanic crust (< 15 km)
Reference note: Massive Mauna Loa is a basaltic shield volcano that rises almost 9 km from the ocean floor to form the world's largest Holocene volcano. Flank eruptions typically occur from the lengthy NE and SW rift zones, and from the Moku'aweoweo summit is caldera, which is within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al., 1989). Almost 90% of…
St. Helens
Location: United States · North America Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2008
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Prior to 1980, Mount St. Helens was a conical volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km breached crater now partially filled by a lava dome. There have been nine major eruptive periods beginning about 40-50,000 years ago, and it has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older…
Popocatepetl
Location: Mexico · Middle America-Caribbean Volcanic Regions
Volcano type: Stratovolcano(es)
Last known eruption: 2026
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to…
Cotopaxi
Location: Ecuador · South America Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2023
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: The symmetrical, glacier-covered, Cotopaxi stratovolcano is Ecuador's most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend to its base. The modern edifice has been constructed since a major collapse sometime prior to about 5,000 years ago. Pyroclastic flows (often confused in historical…
Ruiz, Nevado del
Location: Colombia · South America Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2026
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in…
Etna
Location: Italy · European Volcanic Regions
Volcano type: Stratovolcano(es)
Last known eruption: 2026
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the…
Vesuvius
Location: Italy · European Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 1944
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: One of the world's most noted volcanoes, Vesuvius (Vesuvio) forms a dramatic backdrop to the Bay of Naples. The active cone was constructed within a large caldera of the older Monte Somma edifice, thought to have formed incrementally beginning about 17,000 years ago. The Monte Somma caldera wall has channeled lava flows and pyroclastic flows primarily to the south and west. Eight major explosive eruptions have taken place in the last 17,000 years, often accompanied by large pyroclastic flows and surges, such as…
Santorini
Location: Greece · European Volcanic Regions
Volcano type: Shield(s)
Last known eruption: 1950
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Santorini (Thera), in the Aegean Sea, has steep-walled caldera rim with villages that overlook an active volcanic island in the center of a caldera bay. The circular island group is composed of overlapping shield volcanoes cut by at least four partially overlapping calderas. The oldest southern caldera was formed about 180,000 years before present (BP), followed by the Skaros caldera about 70,000 BP, and then the Cape Riva caldera about 21,000 BP. The youngest caldera formed about 3,600 BP (around 1600 BCE)…
Eyjafjallajokull
Location: Iceland · Atlantic Ocean Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2010
Tectonic setting: Rift zone / Oceanic crust (< 15 km)
Reference note: Eyjafjallajökull (also known as Eyjafjöll) is located west of Katla volcano. It consists of an elongated ice-covered stratovolcano with a 2.5-km-wide summit caldera. Fissure-fed lava flows occur on both the E and W flanks, but are more prominent on the western side. Although the volcano has erupted during historical time, it has been less active than other volcanoes of Iceland's eastern volcanic zone, and relatively few Holocene lava flows are known. An intrusion beneath the S flank from July-December 1999 was…
Nyiragongo
Location: DR Congo · Eastern Africa Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2026
Tectonic setting: Rift zone / Continental crust (> 25 km)
Reference note: The Nyiragongo stratovolcano contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and…
Merapi
Location: Indonesia · Sunda-Banda Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2026
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice,…
Krakatau
Location: Indonesia · Sunda-Banda Volcanic Regions
Volcano type: Caldera
Last known eruption: 2024
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: The renowned Krakatau (frequently misnamed as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This…
Tambora
Location: Indonesia · Sunda-Banda Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 1967
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: The massive Tambora stratovolcano forms the entire 60-km-wide Sanggar Peninsula on northern Sumbawa Island. The largely trachybasaltic-to-trachyandesitic volcano grew to about 4,000 m elevation before forming a caldera more than 43,000 years ago. Late-Pleistocene lava flows largely filled the early caldera, after which activity changed to dominantly explosive eruptions during the early Holocene. Tambora was the source of history's largest explosive eruption, in April 1815. Pyroclastic flows reached the sea on all…
Pinatubo
Location: Philippines · Western Pacific Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2021
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and…
Fujisan
Location: Japan · Northwestern Pacific Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 1708
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: The conical form of Fujisan, Japan's highest and most noted volcano, belies its complex origin. The modern postglacial stratovolcano is constructed above a group of overlapping volcanoes, remnants of which form irregularities on Fuji's profile. Growth of the Younger Fuji volcano began with a period of voluminous lava flows from 11,000 to 8000 years before present (BP), accounting for four-fifths of the volume of the Younger Fuji volcano. Minor explosive eruptions dominated activity from 8000 to 4500 BP, with…
Taal
Location: Philippines · Western Pacific Volcanic Regions
Volcano type: Caldera
Last known eruption: 2026
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Taal is one of the most active volcanoes in the Philippines and has produced some powerful eruptions. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, with several submerged eruptive centers. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all observed eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones. Powerful pyroclastic…
Ruapehu
Location: New Zealand · Tonga-Kermadec Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2007
Tectonic setting: Subduction zone / Continental crust (> 25 km)
Reference note: Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the NW-flank Murimoto debris-avalanche deposit. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been…
Erebus
Location: Antarctica · Antarctic-Scotia Volcanic Regions
Volcano type: Stratovolcano
Last known eruption: 2026
Tectonic setting: Intraplate / Continental crust (> 25 km)
Reference note: Mount Erebus overlooks the McMurdo research station on Ross Island and is the largest of three major volcanoes forming the roughly triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3,200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m, 110-m-deep crater truncates the summit and…
Largest mapped earthquakes since 1900
9.5 · 1960 Great Chilean Earthquake (Valdivia Earthquake)
Date: 1960-05-22
Depth: 25.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
9.2 · The 1964 Prince William Sound, Alaska Earthquake
Date: 1964-03-28
Depth: 25.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
9.1 · 2004 Sumatra – Andaman Islands Earthquake
Date: 2004-12-26
Depth: 30.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
9.1 · 2011 Great Tohoku Earthquake, Japan
Date: 2011-03-11
Depth: 29.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
9.0 · 89 km ESE of Petropavlovsk-Kamchatsky, Russia
Date: 1952-11-04
Depth: 21.6 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.8 · 1906 Ecuador-Colombia Earthquake
Date: 1906-01-31
Depth: 20.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.8 · 2010 Maule, Chile Earthquake
Date: 2010-02-27
Depth: 22.9 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.8 · 2025 Kamchatka Peninsula, Russia Earthquake
Date: 2025-07-29
Depth: 35.0 km
Tsunami catalog flag: Present
USGS event page: Open catalog record
8.7 · 1965 Western Aleutian Islands (Hawadax/Rat Islands) Earthquake
Date: 1965-02-04
Depth: 30.3 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.6 · 1946 Unimak Island, Alaska Earthquake
Date: 1946-04-01
Depth: 15.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.6 · 1950 Assam-Tibet Earthquake
Date: 1950-08-15
Depth: 15.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.6 · 1957 Atka, Alaska Earthquake
Date: 1957-03-09
Depth: 25.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.6 · 78 km WSW of Singkil, Indonesia
Date: 2005-03-28
Depth: 30.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.6 · 2012 Wharton Basin Earthquake
Date: 2012-04-11
Depth: 20.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.5 · 94 km ENE of Vallenar, Chile
Date: 1922-11-11
Depth: 70.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.5 · 1938 Banda Sea Earthquake
Date: 1938-02-01
Depth: 25.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.5 · 1963 Kuril Islands Earthquake
Date: 1963-10-13
Depth: 35.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
8.4 · 1923 Kamchatka, Russia Earthquake
Date: 1923-02-03
Depth: 15.0 km
Tsunami catalog flag: Not present
USGS event page: Open catalog record
10. Rapid Revision Points
- Plates are lithosphere, not merely crust.
- Oceanic lithosphere forms at ridges and is commonly destroyed at subduction zones.
- Transform boundaries conserve lithosphere and generate shallow earthquakes.
- Subduction creates trenches, inclined earthquake zones and volcanic arcs.
- Continental collision creates thick crust, mountains and major earthquakes but usually no continuous volcanic arc.
- Deep earthquakes are diagnostic of subducting slabs.
- Magnitude describes event size; intensity describes local effects.
- Hotspots explain important intraplate volcanoes and age-progressive chains.
- Not every earthquake or volcano lies exactly on a narrow plate boundary.
- A tsunami requires major water displacement, not merely a high earthquake magnitude.
11. Test Yourself
Q1. Which force is commonly regarded as the strongest direct driver of plate motion?
Dense, cold oceanic lithosphere sinking at a subduction zone can pull the rest of the plate behind it.
Q2. New oceanic lithosphere is created mainly at:
Decompression melting at divergent oceanic boundaries creates basaltic crust.
Q3. The Andes are chiefly associated with:
The oceanic Nazca Plate subducts beneath the South American Plate.
Q4. Which boundary normally produces only shallow-focus earthquakes?
Transform faults do not carry a cold slab deep into the mantle, so their earthquakes are shallow.
Q5. The Himalayan mountain system formed primarily through:
India collided with Eurasia, shortening and thickening continental crust.
Q6. The oldest oceanic crust in a basin is generally found:
Oceanic crust becomes progressively older as it moves away from a spreading ridge.
Q7. A Wadati–Benioff zone identifies:
Earthquake foci outline the descending slab beneath an overriding plate.
Q8. Which pair is correctly matched?
The Sunda Trench marks subduction of Indo-Australian oceanic lithosphere beneath the Sunda region.
Q9. Magma at most subduction-zone volcanic arcs is generated because:
Water-rich fluids lower the solidus of mantle rock above the slab.
Q10. Which statement about magnitude and intensity is correct?
Observed shaking depends on distance, building quality and local geology, so intensity varies spatially.
Q11. Hawaii is best explained by:
The Pacific Plate moves over a long-lived mantle melting anomaly, producing an age-progressive island chain.
Q12. Deep-focus earthquakes are most characteristic of:
Only a descending cold slab remains brittle enough to generate earthquakes hundreds of kilometres deep.
Q13. The East African Rift is an example of:
The African continent is stretching and separating into Nubian and Somali plate regions.
Q14. A tsunami-generating megathrust earthquake most commonly occurs at:
Locked subduction interfaces can rupture over huge areas and vertically displace the seafloor.
Q15. Which observation was central to the acceptance of seafloor spreading?
Alternating magnetic anomalies record crust formation and outward movement on both sides of a ridge.
12. Frequently Asked Questions
What is a tectonic plate?
A tectonic plate is a large, coherent slab of lithosphere—the crust plus the rigid uppermost mantle—that moves over the weaker asthenosphere. Plates may contain both continental and oceanic crust.
What causes tectonic plates to move?
Plate motion is driven by gravity and mantle dynamics. Important forces include slab pull from sinking dense lithosphere, ridge push from elevated spreading ridges and tractions associated with mantle convection.
Why do most earthquakes occur near plate boundaries?
Plate motion builds stress where plates lock, collide, separate or slide past one another. When a fault suddenly slips, stored elastic energy is released as seismic waves.
Why are volcanoes common at subduction zones?
Water and other volatiles released from the descending slab lower the melting temperature of the mantle wedge. The resulting magma rises and may feed a volcanic arc.
Why are volcanoes uncommon at continent–continent collision zones?
Continental lithosphere is buoyant and resists deep subduction. Collision mainly thickens and deforms crust, so major mountain belts and earthquakes are more typical than continuous volcanic arcs.
What is the difference between earthquake magnitude and intensity?
Magnitude measures energy released at the source and has one principal value for an event. Intensity describes observed shaking and damage, so it varies from place to place.
What is a Wadati–Benioff zone?
It is an inclined zone of earthquake foci tracing a subducting slab from a trench to depths that may approach 700 kilometres.
Can earthquakes occur inside plates?
Yes. Intraplate earthquakes occur when ancient faults or zones of weakness are reactivated by stresses transmitted through a plate, though they are less common than boundary earthquakes.
Are hotspots plate boundaries?
Usually not. Hotspots such as Hawaii represent localized mantle melting within a plate. As the plate moves over the source, it can form an age-progressive volcanic chain.
Does every undersea earthquake cause a tsunami?
No. A damaging tsunami usually requires substantial, rapid vertical displacement of the seafloor or another large disturbance such as a submarine landslide.
What does this map show?
The map combines PB2002 plate polygons and classified boundary steps, Smithsonian Holocene volcano records, and USGS catalog earthquakes of magnitude 8.0 or greater since 1900. Boundaries and hazards are generalized for education.
13. Sources and Further Reading
- USGS: This Dynamic Earth — foundational plate-tectonics explanations and diagrams.
- USGS Earthquake Catalog — source for the mapped M8.0+ earthquake records.
- USGS GeoJSON feeds — current earthquake-data documentation.
- Smithsonian Global Volcanism Program — global volcano and eruption database.
- Smithsonian VOTW web services — source for mapped Holocene-volcano coordinates and attributes.
- Bird (2003), PB2002 — digital global plate-boundary model used for plate geometry and classified boundary steps.
- NOAA JetStream: Tsunamis — tsunami generation, propagation and safety.
