What is the difference between a caldera and a crater in a volcano

The fractured rock above the magma chamber collapsed to produce a massive crater over six miles across. Centuries of rain and snow filled the caldera, creating Crater Lake. With a depth of feet meters , Crater Lake is the deepest lake in the United States and the ninth-deepest lake in the world. Enlarge image.

Calderas are some of the most spectacular features on Earth. They are large volcanic craters that form by two different methods: 1 an explosive volcanic eruption; or, 2 collapse of surface rock into an empty magma chamber. The accompanying image is a satellite view of one of the most famous calderas - Crater Lake in Oregon. Crater Lake was formed about years ago when an enormous volcanic eruption of Mount Mazama emptied a large magma chamber below the mountain.

Collapse calderas form when a large magma chamber is emptied by a volcanic eruption or by subsurface magma movement. The unsupported rock that forms the roof of the magma chamber then collapses to form a large crater. Crater Lake and many other calderas are thought to have formed by this process. The four-step illustration below explains how the Crater Lake caldera is thought to have formed.

The video on this page shows a table-top model of caldera formation. This would be an excellent activity for teachers to do with their students, or they can simply show the video using computer projection.

Caldera demonstration: This video shows a teaching activity that clearly demonstrates how a caldera is formed. It can be difficult to explain or draw how a caldera forms.

This table-top model is a great demonstration. Teachers can do this activity with their students, or simply show the video in class using computer projection. Geological Survey Open-File Report Explosive Eruptions at Kilauea : Many of Kilauea's pre explosive eruptions that produced significant ash deposits probably happened when the volcano's summit crater was so deep that its floor was below the water table, letting groundwater seep in to form a lake.

Whenever magma erupted into the lake water, violent explosions of steam and volcanic gases resulted, fragmenting the magma into tiny ash particles and driving fast-moving, extremely hot ash-laden steam clouds pyroclastic surges out of the crater. Image and caption by USGS. Eruptions of ash and pumice: The cataclysmic eruption started from a vent on the northeast side of the volcano as a towering column of ash, with pyroclastic flows spreading to the northeast.

Caldera collapse: As more magma was erupted, cracks opened up around the summit, which began to collapse. Fountains of pumice and ash surrounded the collapsing summit, and pyroclastic flows raced down all sides of the volcano. Steam explosions: When the dust had settled, the new caldera was 5 miles 8 km in diameter and 1 mile 1. Groundwater interacted with hot deposits, causing explosions of steam and ash. Today: In the first few hundred years after the cataclysmic eruption, renewed eruptions built Wizard Island, Merriam Cone, and the central platform.

Volcanic materials volcanic rocks and tuff above this chamber collapses inside leaving a huge depression at the top. Calderas can be circular or take any shape because of the magnitude and violent nature of the volcanic activity forming them.

Calderas, in some cases, begin as craters but deepen and expand with heightened volcanic activity that widens the chambers. Some calderas are formed as a result of big and sudden volcanic explosions, a phenomenon that explains their irregular shapes. In both cases, the unsupported ceiling above the empty chamber collapses to fill the gap left behind. Calderas form at the end of the eruption as the empty magma chamber underneath fills.

Almost vertical walls are a key feature of a caldera. Many calderas in the world are filled with water creating small to medium-sized lakes, like Crater Lake in Oregon, US. After volcanic activity, lava at the top of a volcano weakens the rock structure through high pressure and sinks them to form a crater described as a depression at the top with openings for active volcanic activities like lava flow and eruption of volcanic ashes.

The active openings for volcanic activities make the difference between a volcanic crater and a caldera, as some craters occasionally show signs of underneath activities through smoke or steam. Large morphological depressions, occasionally up to 50 km in diameter, are called calderas and are the result of the collapse ofthe volcanic edifice into their own underlying, partially emptied magma chamber. These large, often circular forms with nearly vertical walls are occasionally filled with water.

After the formation of a caldera, the open space at the crater floor is subsequently filled in by more recent lava flows. The reason for the shape of calderas is believed to be the collapse of the roof of a central reservoir of shallow magma.