Topography produced by Volcanism
🌋 Extrusive Volcanic Topography (formed above the Earth’s surface)
- Created when magma erupts as lava and cools on the surface.
- Forms features like shield volcanoes, composite volcanoes, cinder cones, lava plateaus, craters, and calderas.
- Example: Mount Fuji (Japan), Mauna Loa (Hawaii), Deccan Traps (India).
🏔️ ELEVATED FORMS
🛡️ Shield Volcano
These are the largest volcanoes on Earth, and they are formed by highly fluid lava that flows easily over great distances.
📍 If we go to Hawaii and as we hike up the mighty Mauna Loa, we can see the largest shield volcano on Earth and we notice something remarkable here—its gentle slopes. Unlike dramatic, conical peaks, Mauna Loa’s lava flows effortlessly, spreading like honey on a flat surface. The eruptions here are not explosive but resemble a grand lava fountain, where molten rock bubbles up and flows like a river of fire.
📝 Key Features:
✔️ Largest volcanoes on Earth
✔️ Low silica, highly fluid basaltic lava → spreads far and wide
✔️ Not explosive (unless water enters the vent!)
✔️ Example: Mauna Loa, Hawaii
⛰️ Composite Volcano
Now, let’s take a detour to Japan, where we stand in awe of Mount Fuji—a towering peak that perfectly fits our childhood drawing of a volcano. But unlike shield volcanoes, composite volcanoes (or stratovolcanoes) are built layer by layer.
They are the highest volcanic mountains on Earth, created by alternating eruptions of:
🔺 Molten lava
🔺 Volcanic ash
🔺 Rock fragments (tephra)
These layers make stratovolcanoes steep-sided and dangerous. Their magma is thicker and richer in silica, making eruptions explosive. Imagine shaking a soda bottle and suddenly opening the cap—that’s what happens when pressure builds inside these volcanoes.
📍 Traveling to Indonesia, we witness the historic Krakatoa eruption of 1883. The explosion was so massive that its sound was heard thousands of kilometers away! These volcanoes are powerful, unpredictable, and stunning.
📝 Key Features:
✔️ Tallest and steepest volcanic mountains
✔️ Layered structure (lava + ash + tephra)
✔️ Highly explosive eruptions
✔️ Examples: Mount Fuji (Japan), Krakatoa (Indonesia)
🔴 Dome Volcano
Now, let’s visit a different kind of volcanic landform—a dome volcano. Imagine a thick, pasty lava oozing out like toothpaste from a tube. It’s too thick to flow far, so it piles up around the vent, forming a steep, rounded dome.
These volcanoes erupt with moderate intensity but are known for their unpredictable behavior. One moment they are silent, and the next, they explode violently due to trapped gases.
📍 Stromboli, Italy—where glowing lava bubbles rise and burst like fireworks. These eruptions are small but frequent, earning Stromboli the title “Lighthouse of the Mediterranean.”
📝 Key Features:
✔️ Thick, slow-moving lava
✔️ Steep, dome-like structure
✔️ Moderate eruptions but can be explosive
✔️ Example: Stromboli, Italy
💣 Cinder Cone Volcano
- Cinder(a small piece of partly burnt coal or wood that has stopped giving off flames but still has combustible matter in it.) cones are mounds of basaltic fragments.
- Streaming gases carry liquid lava blobs into the atmosphere that rain back to earth around the vent to form a cone.
- The lava blobs commonly solidify, or partially solidify, during flight through the air before landing on the ground. They are called “bombs.”
- The longer the eruption the higher the cone. Some are no higher than a few meters and others rise to as high as 610 meters or more
📝 Key Features:
✔️ Small, steep-sided cones
✔️ Erupt explosively, forming lava “bombs“
✔️ Short-lived compared to other volcanoes
✔️ Example: Parícutin, Mexico
🌋 DEPRESSED FORMS
🕳️ Craters
Now, let’s descend into the heart of a volcano—the crater. When a volcano erupts, it blasts open a funnel-shaped depression at its summit. This is where lava, ash, and gases escape. Think of it as the mouth of a volcano.
📍 At Mount Fuji, we peer into its massive crater, a silent reminder of past eruptions. Some craters are active, while others have become calm, silent voids waiting for their next awakening.
📝 Key Features:
✔️ Funnel-shaped depression at the summit
✔️ Formed by explosive eruptions
✔️ Example: Crater of Mount Fuji, Japan
🏞️ Calderas
Now, imagine a volcano so massive that after a colossal eruption, its entire top collapses into itself, forming a huge, circular depression. This is a caldera.
📍 Let’s visit Oregon, USA, where Mount Mazama once stood tall. But after an enormous eruption, the summit collapsed, creating a deep basin filled with water—Crater Lake.
Calderas are often much larger than craters and can stretch for kilometers. Some, like Yellowstone Caldera, are so massive that they contain entire ecosystems within them.
📝 Key Features:
✔️ Larger than craters, formed by collapse
✔️ Can become lakes (e.g., Crater Lake, USA)
✔️ Example: Caldera of Mount Mazama, Oregon, USA
🪨 Intrusive Volcanic Topography (formed inside the Earth’s crust)
- Magma solidifies beneath the surface, forming large rock bodies.
- Forms features like batholiths, laccoliths, sills, dikes, and lopoliths (already discussed in rocks chapter)
- Example: The Sierra Nevada Batholith (USA), Karnataka’s layered igneous intrusions (India).
Miscellaneous topics
🛁 Geysers – Nature’s Water Cannon
Imagine a giant underground pressure cooker. Deep below the Earth’s surface, magma heats underground water, but instead of escaping immediately, the water gets trapped within a narrow underground passage. As the pressure builds, suddenly—BOOM!—it erupts skyward in a spectacular fountain of hot water and steam.
📍If you visit Yellowstone National Park, USA! Here, we stand before Old Faithful, the world’s most famous geyser. Every 60-90 minutes, it erupts like a natural clock, shooting water up to 50 meters into the sky!
📝 Key Features of Geysers:
✔️ Intermittent eruptions of hot water & steam 🌊💨
✔️ Caused by trapped water heating under high pressure
✔️ Occurs in geologically active regions
✔️ Example: Old Faithful (USA), Strokkur (Iceland), Lady Knox (New Zealand)
🔹 How are they different from hot springs?
A hot spring releases hot water continuously (like an overflowing bathtub), while a geyser erupts only periodically (like shaking a soda bottle and opening it).
💨 Fumaroles
Ever seen steam rising from the ground, making it look like the Earth itself is breathing? That’s a fumarole—a volcanic vent that releases gases like steam, sulfur, and carbon dioxide.
📍 Now, let’s head to Mount Etna, Italy. From a distance, the mountain looks like it’s covered in clouds, but these are actually fumaroles releasing volcanic gases! The smell of sulfur (like rotten eggs) fills the air, a reminder of the molten rock beneath.
📝 Key Features of Fumaroles:
✔️ Emits gases & water vapor instead of liquid water 🌫️
✔️ Occurs near volcanic areas (even after eruptions end)
✔️ Often gives off a strong sulfur smell 🧅
✔️ Example: Mount Etna (Italy), Yellowstone (USA), Kamchatka (Russia)
🌊 Hydrothermal Vents
Now, let’s dive deep—way down to the bottom of the ocean. Here, in complete darkness, lies one of Earth’s most mysterious landscapes: hydrothermal vents.
Imagine cracks in the seafloor where superheated water (400°C!) gushes out, filled with minerals. As the water meets the icy deep-sea temperatures, it creates towering chimney-like structures known as black smokers, billowing out dark clouds of mineral-rich steam.
📍 We are now in the Mid-Atlantic Ridge, witnessing an alien-like ecosystem. Despite the extreme conditions, life thrives here—giant tube worms, bizarre shrimp, and even bacteria that don’t rely on sunlight but instead use chemical energy from the vent water to survive. 🌊🐛
📝 Key Features of Hydrothermal Vents:
✔️ Found at tectonic boundaries & ocean floors 🌊
✔️ Release mineral-rich, superheated water
✔️ Home to unique deep-sea ecosystems 🦐
✔️ Example: Mid-Atlantic Ridge, Pacific Ocean, Indian Ocean
🔹 Why do hydrothermal vents exist?
Because Earth’s crust is constantly shifting! Where plates move apart, magma rises and heats trapped ocean water, creating these vents.
