Plate tectonics FAQ

There are seven major tectonic plates and many smaller ones. The PB2002 model used on this site counts 52 plates: 7 major, 13 minor and 32 microplates. Other models give different totals depending on how they treat small blocks and broad zones of deformation. Browse all 52 in the plate directory.

The Pacific, African, Antarctic, North American, Eurasian, Australian and South American plates. Many textbooks combine the Australian and Indian plates into one Indo-Australian Plate. Together the seven major plates cover about 81% of Earth's surface.

The Pacific Plate is the largest, with an area of about 104.6 million square kilometers, roughly 20.5% of Earth's surface. It is almost entirely ocean floor and is nearly twice the size of the next largest plate, the African Plate.

In the PB2002 model the smallest plate is the Manus Plate in the Bismarck Sea north of Papua New Guinea, at about 8,200 square kilometers. The next smallest is the Galapagos Plate, at about 14,600 square kilometers. Among commonly taught plates, the Juan de Fuca Plate off the north-western United States is one of the smallest.

In PB2002 the Tonga Plate moves fastest relative to its neighbors, averaging about 11.4 cm per year along its boundaries. At the Tonga Trench it converges with the Pacific Plate at up to about 26 cm per year, the fastest relative motion in the model. Among the major plates, the Pacific Plate is fastest, averaging about 7.3 cm per year along its boundaries.

Among the major plates, the African Plate is slowest in PB2002, averaging about 1.8 cm per year relative to its neighbors along its boundaries. The Eurasian Plate is close behind at about 2.0 cm per year. Plates with few subducting edges tend to move slowly.

Most plates move between about 2 and 10 cm per year relative to their neighbors, about as fast as fingernails grow. Across all subduction zones in PB2002 the average relative speed is about 6.2 cm per year, and across all spreading ridges about 4.7 cm per year. The Atlantic Ocean widens by about 2.5 cm per year.

Almost all of the United States, about 98.9% of its area in PB2002, lies on the North American Plate. The rest is on the Pacific Plate, including Hawaii and the strip of coastal California west of the San Andreas Fault. Southern Alaska sits above the Aleutian subduction zone, where the Pacific Plate sinks beneath North America.

The United Kingdom lies entirely on the Eurasian Plate, far from any plate boundary. The nearest boundary is the Mid-Atlantic Ridge to the west, where Eurasia and North America are moving apart. That is why the UK has only small earthquakes and no active volcanoes.

Most of India, about 91% of its area in PB2002, lies on the Indian Plate. The far north, in the Himalaya, extends onto the Eurasian Plate. The Indian Plate is pushing into Eurasia at an average of about 4.7 cm per year in PB2002, which is still raising the Himalaya.

In PB2002, Japan lies mostly on two plates: north-eastern Honshu and Hokkaido on the Okhotsk Plate (about 55% of its area) and south-west Japan on the Amur Plate (about 42%). Many textbooks simplify these to the North American and Eurasian plates. The Pacific Plate and the Philippine Sea Plate subduct beneath Japan from the east and south.

Australia lies entirely on the Australian Plate, one of the seven major plates. Older textbooks call it the Indo-Australian Plate, but PB2002 and many modern models treat the Indian and Australian plates as separate plates joined by a broad zone of deformation.

Iceland sits on two plates. In PB2002, about 56% of the island lies on the North American Plate and about 44% on the Eurasian Plate. The Mid-Atlantic Ridge crosses the island, and a hotspot beneath it adds extra volcanic activity.

New Zealand straddles a plate boundary. PB2002 puts about 43% of its area on the Pacific Plate, about 38% on the Australian Plate and about 19% on the small Kermadec Plate. The Alpine Fault on the South Island and the Hikurangi subduction zone off the North Island mark the boundary.

Most of Mexico, about 93% of its area in PB2002, lies on the North American Plate. The Baja California peninsula is on the Pacific Plate. Off the south coast, the Cocos Plate and Rivera Plate sink beneath Mexico, causing large earthquakes and feeding its volcanoes.

Most of Turkey lies on the Anatolian Plate, which covers about 59% of the country in PB2002. The north and east are on the Eurasian Plate, and the south-east is on the Arabian Plate. The Anatolian Plate is squeezed westward between them along the North and East Anatolian faults.

Convergent boundaries, where plates move toward each other; divergent boundaries, where they move apart; and transform boundaries, where they slide past each other. In PB2002 about 36% of boundary length is divergent, 35% convergent and 28% transform.

The boundaries between the 52 plates of PB2002 add up to about 260,800 km, more than six times the length of the equator. Oceanic spreading ridges are the longest single class, at about 67,300 km, followed by subduction zones at about 51,500 km. See plate boundaries for all seven classes.

As plates move, friction locks the faults along their edges. Stress builds up in the surrounding rock until it overcomes the friction, and the fault slips suddenly, sending out seismic waves. The largest earthquakes happen on subduction zone megathrusts, such as the 1960 Chile earthquake (M9.5). Explore them on the earthquake map.

Most volcanoes form where the mantle melts at plate boundaries. At divergent boundaries, rising mantle melts as the pressure on it drops. At subduction zones, water released from the sinking plate lowers the melting point of the mantle above it. A third group forms over hotspots, such as Hawaii. See the volcano map.

Plates move because Earth's interior is losing heat. The strongest force is slab pull, the weight of old, cold oceanic plate sinking into the mantle at subduction zones. Ridge push at mid-ocean ridges and drag from the flowing mantle also contribute. Plates attached to long subducting slabs, such as the Pacific and Nazca plates, move fastest.

Not on any timescale that matters to people. Plates will keep moving as long as Earth's interior is hot enough to drive mantle convection and old ocean floor keeps sinking at subduction zones. Over billions of years, as the planet cools, plate tectonics is expected to slow and could eventually stop.

Many geologists expect the continents to gather into a new supercontinent in a few hundred million years, but its shape is a matter of hypothesis. Proposed versions include Pangaea Proxima, if the Atlantic closes, and Amasia, if the Americas and Asia meet across the Arctic. Read more about Pangaea and earlier supercontinents.

Pangaea was a supercontinent that joined nearly all of Earth's land into one mass. It was assembled by about 335 million years ago and began to break apart about 200 million years ago, opening the Atlantic Ocean. See Pangaea for the evidence and the breakup story.

The Ring of Fire is a belt of subduction zones, volcanoes and earthquake zones around the Pacific Ocean. It is commonly cited as holding about 75% of Earth's active volcanoes and roughly 80-90% of its earthquakes. Four of the five magnitude 9 earthquakes since 1900 struck on it.

GPS stations fixed to bedrock measure plate motion directly, to within millimeters per year. Magnetic stripes on the ocean floor record how fast plates have separated over millions of years, and chains of hotspot volcanoes such as Hawaii trace a plate's path. These independent methods agree closely.

Older textbooks treat it as one plate. PB2002 and many modern models split it into the Indian Plate and the Australian Plate, because the two move slightly differently and the crust between them in the central Indian Ocean is deforming. The 2012 Wharton Basin earthquake (M8.6) struck inside that zone.

Yes, though they are much less common than at plate boundaries. Plates are not perfectly rigid, and old faults inside them can slip under stress transmitted from the plate edges. The New Madrid earthquakes of 1811-1812 in the central United States are a well known example.