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How does lava viscosity affect the shape of a volcano?

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A car drives along the Trans-Canada Highway with Mount Sir Donald's sharp, snow-capped peak rising above forested slopes in the Selkirk Mountains, British Columbia. — mountain Mount Sir Donald in the Selkirk Mountains, British Columbia, looms above a segment of the Trans-Canada Highway.

Lava viscosity is a primary factor in determining the shape and structure of a volcano. Viscosity, which is largely influenced by silica content and temperature, dictates how lava flows and how gases escape, ultimately shaping the resulting landform.123

Low-Viscosity (Fluid) Lava: Magmas with lower silica content, such as basalt, are highly fluid. This allows the lava to travel long distances from the vent, creating broad, gently sloping structures known as shield volcanoes. Because the lava is fluid, gases can escape relatively easily, often resulting in non-explosive, effusive eruptions.1243
High-Viscosity Lava: Magmas rich in silica, such as andesite, dacite, and rhyolite, are highly viscous. This thick lava does not flow easily and tends to pile up around the vent. When extremely viscous, it forms steep-sided lava domes. Because the high viscosity traps gases, these volcanoes are often associated with violent, explosive eruptions that can build stratovolcanoes through alternating layers of ash and lava.153