Volcanoes shape Earth's surface in dramatic ways. From smooth lava flows to explosive ash clouds, volcanic activity creates diverse landforms. Understanding these formations helps us grasp the power and complexity of volcanic processes.

Lava composition and eruption style are key factors in shaping volcanic landscapes. Silica-rich magmas produce steep domes and explosive eruptions, while low-silica lavas form gentle shield volcanoes. These differences create Earth's varied volcanic terrains.

Volcanic Landforms

Main volcanic landforms

• Lava flows form when molten rock (lava) pours out from a volcanic vent or fissure and spreads across the landscape (Kilauea, Hawaii)
  • Pahoehoe lava creates smooth, ropy, or billowy surface textures as it cools
  • A'a lava produces rough, jagged, and clinkery surface textures due to faster cooling and higher viscosity (Craters of the Moon, Idaho)
• Lava domes grow as viscous, silica-rich lava accumulates around the volcanic vent, forming steep-sided, rounded or flat-topped structures (Mount St. Helens, Washington)
• Pyroclastic flows are high-density mixtures of hot volcanic ash, pumice, rock fragments, and gas that move rapidly downslope at speeds up to 100 km/h and temperatures of 100-800°C (Mount Pinatubo, Philippines)
• Lahars are volcanic mudflows or debris flows consisting of volcanic ash, rock debris, and water from melted snow, heavy rain, or a crater lake; they can travel great distances at high speeds causing significant damage (Nevado del Ruiz, Colombia)

Volcanic ash and debris

• Volcanic ash consists of fine particles (less than 2 mm) of pulverized rock and glass formed by explosive fragmentation of magma or rock during eruptions; it can be transported long distances by wind causing respiratory issues, damage to infrastructure, and disruption of air travel (Eyjafjallajökull, Iceland)
• Pumice is a highly vesicular (porous) volcanic rock with low density formed by rapid cooling of gas-rich, felsic magma during explosive eruptions; it is often light-colored and can float on water (Mono Lake, California)
• Scoria is a moderately vesicular volcanic rock with higher density than pumice, formed by cooling of gas-rich, mafic magma during mildly explosive eruptions; it is often dark-colored with a rough, cindery surface (Sunset Crater, Arizona)
• Environmental impacts of volcanic ash and debris include smothering vegetation, contaminating water sources, causing respiratory issues for humans and animals; pumice and scoria deposits can improve soil drainage and fertility long-term but may initially hinder plant growth

Factors Influencing Volcanic Landforms

Lava composition and landform morphology

• Lava composition plays a key role in determining landform morphology
  • Felsic (silica-rich) lavas have high viscosity and are often associated with steep-sided lava domes and explosive eruptions (Chaiten, Chile)
  • Mafic (silica-poor) lavas have low viscosity and are often associated with gently-sloping shield volcanoes and effusive eruptions (Mauna Loa, Hawaii)
• Viscosity is a measure of a fluid's resistance to flow and is influenced by factors such as:
  1. Silica content: Higher silica content leads to higher viscosity
  2. Temperature: Lower temperatures result in higher viscosity
  3. Gas content: Higher gas content can increase or decrease viscosity depending on the lava composition and gas escape rate
• Morphology is shaped by lava viscosity
  • Low-viscosity lavas tend to produce thin, extensive lava flows and shield volcanoes with gentle slopes (Olympus Mons, Mars)
  • High-viscosity lavas tend to produce thick, short lava flows, steep-sided lava domes, and composite volcanoes (Mount Fuji, Japan)

Eruption types and resulting landforms

• Effusive eruptions are characterized by the relatively gentle outpouring of lava and are associated with mafic, low-viscosity magmas
  • Resulting landforms include shield volcanoes, lava plains and plateaus (Columbia River Basalt Province), and lava tubes and channels (Thurston Lava Tube, Hawaii)
• Explosive eruptions are characterized by the violent fragmentation and ejection of magma and rock, and are associated with felsic, high-viscosity magmas or the interaction of magma with water
  • Resulting landforms include:
    1. Composite volcanoes (stratovolcanoes) built by alternating layers of lava flows, pyroclastic material, and ash (Mount Rainier, Washington)
    2. Lava domes formed by the extrusion of viscous lava (Novarupta, Alaska)
    3. Pyroclastic flows and surges of hot ash, pumice, and gas (Mount Vesuvius, Italy)
    4. Calderas formed by the collapse of a volcano's summit or the emptying of its magma chamber (Yellowstone, Wyoming)