Earthquakes and Volcanoes – Vocabulary Flashcards

Vocabulary flashcards covering key terms from the lecture notes on earthquakes and volcanoes.

Earthquakes

A sudden release of energy within the Earth that produces ground shaking.

Fracture/Crack

A crack in the Earth's crust that can initiate earthquake activity.

Folding

Rocks deformed by compressional forces that bend without breaking.

Faulting/Downward Movement

Rocks moving along fractures, either up or down, during an earthquake.

Subduction

Denser tectonic plate sinking beneath another plate, triggering earthquakes.

Volcanoes as a Cause

Volcanic activity can trigger earthquakes through magma movement and associated processes.

Upliftment

Upward movement of landmasses that can contribute to seismic events.

Fore Shock

An initial, smaller quake that occurs before the main earthquake.

Main Shock

The primary, most powerful earthquake event of a sequence.

After Shock

Subsequent, smaller earthquakes following the main shock as the system settles.

Hard Rock/Stable Landmass

Rocky ground that resists seismic energy, typically causing lesser damage.

Loose Soil/Alluvium/Sediment

Unstable ground that transmits energy quickly and can cause greater destruction.

Soil Liquefaction

Water-saturated soil behaving like a liquid during shaking, increasing damage.

Modified Mercalli Scale (MMS)

A 1–12 scale that measures earthquake intensity based on observed impacts; subjective.

Richter Scale

A magnitude scale that measures energy released; each whole-number step represents about 10x more energy.

Shallow Focus

Earthquakes with focus at depths of 0–60 km.

Intermediate Focus

Earthquakes with focus at depths of 60–300 km.

Deep Focus / Plutonic Earthquake

Earthquakes with focus at depths from about 300 km to over 700 km; 'plutonic' means deep in the earth.

Volcanic Earthquake

Earthquake caused by volcanic processes such as magma movement.

Tectonic Earthquake

Earthquake resulting from plate movements and rock fracturing.

Isostatic Earthquake

Quake due to isostatic adjustments in the crust (e.g., mountain building or large-scale human changes).

Artificial/Man-made Earthquake

Earthquake caused by human activities such as bombing or underground mining.

Circum-Pacific Belt (Pacific Ring of Fire)

Belt with high volcanic and seismic activity; contains about 65% of the world's earthquakes.

Mid-Continental Belt (Alpine-Himalayan Belt)

Region of earthquakes mainly due to continent–continent convergence; about 21% of earthquakes.

Mid-Atlantic Belt

Seismic region associated with divergent boundaries and mid-ocean ridges; fissure-type activity common near Iceland.

Landslides

Secondary hazard triggered by earthquakes in hilly or mountainous terrain.

Mudslides

Earthquake-triggered flow of water-saturated sediments down slopes.

Avalanches

Rapid downward movement of snow and ice triggered by shaking.

Dam Failures

Earthquakes can cause dam breaches leading to floods.

GLOFs (Glacier Lake Outburst Floods)

Sudden floods caused by breaking of glacial barriers after quakes.

Fires

Electrical or gas-related fires sparked by earthquakes.

Structural Collapse

Destruction and collapse of buildings and infrastructure.

Tsunami

Giant ocean waves generated by earthquake-induced seafloor movement.

Zone 2 Seismic Zone (India)

Low-risk seismic zone in India (part of the Zone 2–5 classification).

Zone 5 Seismic Zone (India)

Very high-risk seismic zone in India, notably the Himalayas and Northeast region.

Intraplate Earthquakes

Earthquakes occurring away from main fault boundaries due to regional faults.

Himalayan Region

High-risk area in India where the Indian plate collides with the Eurasian plate.

Northeast India

High seismic risk region in India due to plate interactions.

Indian Plate–Eurasian Plate Collision

Tectonic collision driving major seismicity in the region.

Tephra

Fragmented material ejected during volcanic eruptions (umbrella term for eruptive products).

Gases in Eruptions

Volcanic gases such as sulfur, nitrogen, CO2, and water vapor released during eruptions.

Cinders (Phoria)

Fragmental volcanic rock (2–64 mm) with many gas bubbles; porous and lightweight.

Lapilli

Volcanic fragments (2–64 mm) denser and less porous than cinders.

Volcanic Bomb

Large volcanic ejecta capable of causing damage.

Pyroclastic Rock

Solidified fragments produced by explosive volcanic eruptions.

Central Eruption (Explosive)

Lava erupts from a central vent; varies in explosiveness.

Hawaiian Type

Lava is less viscous, flows easily, and eruptions are relatively gentle.

Strombolian Type

Rhythmic, continuous eruptions; more violent than Hawaiian but less than Vulcanian.

Vulcanian Type

Explosive eruptions with high-viscosity lava and strong blasts.

Pelean Type

Most violent and dangerous eruption type.

Vesuvian Type

Explosive eruptions with very large magma outbursts.

Fissure Eruption

Magma erupts through long cracks; lava flows are typically quiet and widespread.

Basaltic Lava

Low-silica, low-viscosity lava common in fissure eruptions.

Iceland (Fissure Eruptions)

Region famous for fissure eruptions along the Mid-Atlantic Ridge.

Lava Viscosity

Viscosity controls lava flow: higher viscosity = thicker, more explosive lava.

More Viscous Lava

Lava with high silica content; sticky and forms domes.

Less Viscous Lava

Low-silica lava; fluid flows to form broad, shield volcanoes.

Active Volcano

Volcano that erupts continuously or frequently.

Dormant

Currently inactive but could erupt again.

Extinct

Volcano with no expected future eruptions.

Composite Cones (Strata Cones)

Tall, layered volcanoes built from viscous lava and tephra; highly conical.

Cinder and Ash Cones

Cones formed from loose tephra and ash with relatively low height.

Basic Lava Cones

Cones formed by less viscous, basaltic lava spreading widely.

Acid Lava Cones

Cones formed by highly viscous lava rich in silica.

Parasitic Cone

Small cones formed on a volcano from secondary vents.

Crater

Depression at the mouth of a volcanic vent created during eruptions.

Caldera

A large, deep volcanic depression formed by crater enlargement or collapse after major eruptions.