10 incredible facts about volcanoes you didn't know

Volcanoes are often reduced to orange lava, ash clouds and disaster films. That view misses their quieter powers: creating islands, feeding deep-sea ecosystems, altering weather and leaving behind hot springs, fertile soil and valuable minerals. Some of the most remarkable discoveries come from the seafloor, Mars or the chemistry of ash rather than a spectacular cone.

Magma forms below the surface and can remain a mixture of melted rock, crystals and gas. When pressure drops or pathways open, gas bubbles expand and propel material upward. The material becomes lava after eruption, while ash and pumice may travel hundreds or thousands of kilometres. A quiet-looking summit can therefore influence cities and aircraft far beyond its base.

Australia adds another layer: the continent has hundreds of ancient volcanoes and crater lakes, yet no volcano is currently erupting on the mainland. From Melbourne's volcanic parks to the blue maar lakes of Mount Gambier, these landscapes reveal how a region can look settled while preserving evidence of fire beneath it. Ten discoveries show why volcanoes belong in daily conversation, not just disaster coverage.

How volcanoes build and reshape land

A volcano is not simply a mountain with a crater. At some volcanoes, magma collects in chambers within fractured crust; at others, it erupts directly through fissures. The resulting structures can include tall cones, broad shields, calderas and underwater edifices. Eruptions also deposit ash, lava and rock fragments in layers, building new ground while burying older terrain.

Most new oceanic crust is born at underwater ridges where tectonic plates separate. As magma cools, it creates basalt that becomes the foundation for future continents. When an eruption reaches the surface, it may form a black basalt island or a pale volcanic cone. Repeated eruptions can grow either one into a large landmass, although waves, erosion and coral eventually wear many away.

Calderas form after a large eruption empties part of a magma system and the unsupported roof collapses. Some later refill with magma, while others become lakes or hydrothermal fields. A crater therefore records only one chapter: the landscape may contain older lava flows, younger ash beds and evidence that groundwater has been heated for centuries.

Surprises hiding in volcanic geology

The first five discoveries challenge the picture of volcanoes as isolated peaks. They show a hidden network of creation on the ocean floor, an animal-shaped giant on Mars and a famous American hotspot that does not work like a household tap.

The evidence for these systems comes from unusual places. Submersibles visit vents that people cannot reach, orbiters measure heat on distant worlds and geologists examine crystals for clues about conditions deep underground.

• Most of the ocean floor is volcanic rock. More than 80 per cent of it formed at spreading ridges or hotspot volcanoes, continually adding and recycling sections of the Earth's crust beneath the sea.
• An underwater eruption can create a new island. Iceland's Surtsey rose from the Atlantic in 1963 and was soon colonised by seabirds and marine life, demonstrating how quickly life can establish itself on fresh volcanic rock.
• The solar system's largest volcano is on Mars. Olympus Mons rises about 22 kilometres above its base and spans roughly 600 kilometres, making it a vast shield even by planetary standards.
• One lava lake is a global outlier. Nyiragongo in the Democratic Republic of the Congo is often identified as the world's largest persistent lava lake, with molten lava continuously visible near the summit.
• Yellowstone's magma is not a giant underground lake. The caldera is roughly 70 kilometres long, while geologists describe a hot, crystal-rich system containing only small pockets of fully molten rock.

Volcanic lightning and extreme heat add cinematic drama, but these processes reveal the bigger story: volcanoes are active parts of the planet's machinery. Viewers who enjoy unusual science can also explore fascinating science reads when the real world fails to provide a live eruption.

Volcanoes across Australia and nearby shores

Australia currently has no volcano in eruption, but its geological record is extensive. Ancient intraplate hotspots and rifts produced volcanoes across eastern Australia and South Australia; many are now worn down, while others preserve steep volcanic necks and water-filled maars. “Dormant” means a volcano could erupt again, yet Australia's mainland volcanoes are generally considered dormant or extinct rather than active.

Melbourne's western suburbs contain ancient volcanic geology, and Albert Park Lake occupies a maar basin. Around Mount Gambier, Blue Lake and several other crater lakes sit within a younger volcanic complex. Local councils and regional tourism businesses use these landscapes for walking, education and recreation, giving an old eruption a practical role in the modern local market.

Sydney sits on sedimentary rocks of the Sydney Basin rather than an active cone, but Australian travellers can still meet volcanic hazards indirectly. Airlines using Sydney and Melbourne hubs follow Volcanic Ash Advisory Centre notices, particularly on routes near New Zealand. Across the Tasman, the active Taupō zone and Auckland's volcanic field make careful planning routine for Australian visitors. Australia Day fireworks over Sydney Harbour, by contrast, are carefully planned bursts, unlike the unpredictable geology beneath them.

Eruptions that changed the world

The second group of discoveries concerns eruptions with effects far beyond their source. Some altered global climate, one reshaped scientific thinking and another injected an enormous quantity of ocean water into the atmosphere.

Each event also exposes a different hazard. Scale, sideways blast, long-lived lava and atmospheric chemistry can look very different in the record, yet all demand attention to what lies beneath apparently quiet ground.

• Tambora produced the largest eruption in recorded history. The Indonesian volcano's 1815 VEI 7 event overwhelmed observers with ash and debris, cooled the globe and helped create the “year without summer” of 1816.
• Krakatoa's final blast circled the planet. The 1883 eruption generated a pressure wave that travelled around Earth several times, while its roar was heard roughly 4,800 kilometres away.
• Mount St Helens erupted sideways. On 18 May 1980, a huge landslide removed the volcano's north flank and exposed pressurised magma, producing a lateral blast that flattened forest across about 600 square kilometres.
• The Deccan Traps altered life on Earth. Vast eruption episodes around 66 million years ago covered western India with immense basalt flows; geological evidence strongly supports their role in the end-Cretaceous mass extinction.
• Hunga Tonga reached into the stratosphere. Its 2022 underwater eruption injected about 146 teragrams of water vapour high into the atmosphere, the largest such injection measured in the modern observational era.

These events show why size alone is a poor guide to danger. A colossal fissure can flood an atmosphere, while a seemingly smaller mountain can unleash a lateral blast, ashfall and landslides that keep moving after the first plume rises.

Why eruptions matter beyond the drama

An eruption can cool the lower atmosphere for a few years when sulfate aerosols scatter sunlight, while volcanic carbon dioxide has a much longer lifetime. Human emissions now dominate the global carbon budget, so blaming volcanoes for climate change reverses the scale of the problem. Their climate influence is real, especially in the year or two after a major eruption, but temporary.

Volcanic landscapes also support geothermal energy, mineral deposits, fertile farms and tourism. Porous ash can retain moisture, and hot water circulating through rock helps form valuable copper, gold and lithium associations. These resources turn “dangerous ground” into economically useful terrain for communities able to manage access and emissions.

Modern forecasting combines satellites, seismometers, gas sensors and reports from farmers, fishers and park staff. Local knowledge often reveals changes that instruments miss, such as unusual gas, ground movement or a change in a spring. That partnership matters in Australian emergency planning, where bushfire, dust and heat warnings are already part of everyday communication.

Turn volcanic knowledge into a safe adventure

Before any trip, check official monitoring and local advice. In Australia, use Geoscience Australia and state emergency information; in New Zealand, follow GeoNet and Civil Defence alerts. Treat access restrictions as firm instructions, learn the difference between an alert level and a visible eruption, and prepare for ash, rain, poor visibility and sudden road closures.

A domestic outing can begin close to home with a guide to Melbourne's maar landscapes or Mount Gambier's crater lakes. For a longer journey, Tongariro's monitored trails in New Zealand offer stark volcanic scenery, provided walkers respect the current alert level. Carry water, suitable footwear, a mask and a charged phone, and keep well clear of vents, crater rims and unstable slopes.

Save this guide, share a discovery with a fellow traveller, and put one carefully researched volcanic destination on your next itinerary. Check the alerts on the day, follow every local rule, and leave the landscape intact for the people and eruptions that follow.