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Unit 6: Sound and space

Changes in the Earth — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 9 parts Lesson 5 of 14 1 quiz

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

Changes in the Earth — HIA INTERNATIONAL notes: Explain how plate movement forms fold mountains, volcanoes and earthquakes.Plate boundary = a place where tectonic plates meet.Change — geological change happens at plate boundaries because the plates are always moving.Speed — some …

  • Pacific Ring of Fire
  • Magma compared with lava
  • Violent eruptions
  • Active, dormant and extinct
  • Weathering
  • Igneous rock

Section 1 of 9Plate boundaries

Plate boundary
Plate boundary a place where tectonic plates meet.
Change
  • Change geological change happens at plate boundaries because the plates are always moving.
Speed
  • Speed some change takes millions of years and some is sudden and violent.
Pacific Ring of Fire
  • Pacific Ring of Fire the area around the Pacific Ocean with many volcanic eruptions and earthquakes.

Section 2 of 9Types of plate movement

MovementWhat happensResult
Plates moving togetherOne plate may slide under the other (subduction) and its rock melts in the mantleFold mountains, volcanoes
Plates moving apartPlates crack when thin; lava erupts from the mantle and hardens to new crustVolcanoes and new crust
Plates sliding pastFriction makes plates stick, pressure builds and is released violentlyEarthquakes

Section 3 of 9Fold mountains

Formation
  • Formation when plates move together, rocks crumple and fold upwards.
Location
  • Location can form under the ocean or on land.
Youngest
  • Youngest the Himalayas and Rocky Mountains are 10 to 25 million years old.
Oldest
  • Oldest the Ural Mountains are more than 200 million years old.

Section 4 of 9Volcanoes

Volcanoes
Formation
  • Formation magma from the mantle rises through cracks in the crust at plate boundaries.
Magma compared with lava
  • Magma compared with lava magma is liquid rock underground; lava is liquid rock on the surface.
Growth
  • Growth lava and ash harden into new rock, so each eruption makes the volcano bigger.
Parts
  • Parts main vent, secondary vent, crater, layers of ash and lava, and ash cloud.
Violent eruptions
  • Violent eruptions thick magma with dissolved gas builds pressure;
    • they can cause avalanches, earthquakes and tsunamis.
Active, dormant and extinct
  • Active, dormant and extinct active volcanoes may erupt at any time, dormant ones have not erupted for a very long time,
    • and extinct ones will not erupt again.

Section 5 of 9Earthquakes

Cause
  • Cause pressure builds up at plate boundaries until the rocks suddenly move.
Magnitude
  • Magnitude the size of an earthquake, which depends on the size of the faults and how far the rocks move.
Range
  • Range from tiny ones recorded only on instruments to violent ones that move rocks tens of metres in seconds.

Section 6 of 9Weathering, erosion and rock formation

Weathering
  • Weathering breaks rock down in place, e.g. freeze–thaw as water in cracks freezes and expands.
Erosion
  • Erosion moves rock fragments by water, wind or ice.
Igneous rock
  • Igneous rock forms when magma or lava cools and crystallises.
Sedimentary rock
  • Sedimentary rock forms when layers of sediment are compacted and cemented.
Metamorphic rock
  • Metamorphic rock forms when heat or pressure changes existing rock without melting.

Section 7 of 9Modelling plate movement

1Cloth
  • Cloth pushing your hands together makes it fold, like fold mountains.
2Paper sheets
  • Paper sheets one sliding over the other models subduction.
3Modelling clay
  • Modelling clay pushing two pieces together makes ridges.
4Chocolate bars with soft centres
  • Chocolate bars with soft centres show crumpling when pushed together.

Section 8 of 9Key terms

TermMeaning
Plate boundaryWhere tectonic plates meet.
SubductionOne plate sliding underneath another.
Fold mountainA mountain formed when crumpled rocks fold upwards.
MagmaLiquid rock underground.
LavaLiquid rock at the surface.
MagnitudeThe strength of an earthquake.
EarthquakeA sudden violent movement of rocks at a plate boundary.

Section 9 of 9Exam technique

1
Tectonic plates never move — they always move, in different ways.
2
Lava and magma are the same — magma is underground and lava is at the surface.
3
Extinct and dormant volcanoes are the same — dormant ones may erupt again.
4
Earthquakes happen only at the surface — they happen when pressure at plate boundaries is suddenly released.

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