Crater Lake National Park

Front 1

dacite

Back 1

an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite

Front 2

pumice

Back 2

A very light and porous volcanic rock formed when a gas-rich froth of glassy lava solidifies rapidly. A typical pumice contains so much trapped air that I can float; composition is usually of rhyolite or trachyte

Front 3

scoria

Back 3

highly vesicular, dark colored (extrusive igneous) volcanic rock that may or may not contain crystals (phenocrysts). It is typically dark in color

Front 4

tuff

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a general term for consolidated rocks made up of pyroclastic fragments of various sizes; formed through solidification of volcanic dust

Front 5

volcanic bomb

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mass of molten rock, formed when a volcano ejects viscous fragments during and eruption. They cool in solid fragments before they reach the ground.

Front 6

welded tuff

Back 6

glass shards, hot ash, pumice and cinders have been fused by hot gases and the weight and heat of overlying materials; composition is highly siliceous

Front 7

Describe the events that led to the formation of the caldera at Mt. Mazama (Crater Lake), Oregon.

Back 7

It grew during the Pleistocene, while alpine glaciers advanced and retreated on its slopes. From its foundation rocks at the base, Maxama rose approximately 11,000 feet above sea level. The cone was broader and less steep because the subsidaiary vents and overlapping cones gave the volcano a bulky, irregular shape. Associated with the construction and destruction of Mazama are a variety of extrusive and intrusive features.

Front 8

Devils Backbone

Back 8

The Devils Backbone is a vertical wall of dark andesite lining the cliff face and measuring about 1,000 feet long by 50 feet across near the top. A dike formed by molten lava that created and filled cracks, as it forced its way up through the rock and then solidified. It has been left standing by the erosion of the surrounding material.

Front 9

Hillman Peak

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The highest point on the rim, at 8,156 feet elevation. Hillman Peak was formed as a parasitic cone when a vent opened on the side of Mount Mazama. The collapse of the parent peak cut Hillman in half, exposing its inner structure

Front 10

Llao Rock

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The thickest sheet of lava on Crater Lake forms this imposing cliff. Formed by a massive rhyodacide flow that came from near the bottom of a satellite cone that exploded

Front 11

Mt. Scott

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Following Mazama's climactic eruption, the summit of Mount Scott became the highest point in the immediate vicinity with an elevation of 8,929 feet. A s

Front 12

Phantom Ship

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older eroded dike or conduit remnant. It is thought to have been formed by a lava flow that filled a glacial trough but more recent evidence indicates that the flow was emplaced in an explosion crater. Once covered by the younger volcano and only exposed when the caldera formed.

Front 13

The Pinnacles

Back 13

an area of tall spires about 5 miles southeast of the rim, are erosional remnants of tuff deposits, 200-300 feet thick, ejected in flaming ash flows during the climactic eruptions. Fused by hot gasses escaping through many feet of ash after the climactic eruption

Front 14

Wizard Island

Back 14

large volcanic cinder cone in crater lake formed by caldera from eruptions after Mazama’s collapse

Front 15

During what epoch did Mt. Mazama form?

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Pleistocene (middle and late)

Front 16

What was the approximate maximum elevation attained by Mt. Mazama?

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11,000 above sea level

Front 17

How many thousands of years ago did the Mazama caldera form?

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7,000

Front 18

How wide and how deep was the caldera when it formed?

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5 miles wide, 4,000 feet deep

Front 19

Describe the origin and appearance of Kerr Valley and Sun Notch at Crater Lake National Park.

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Kerr Valley and Sun Notch on the southeast side are spectacular U-shaped toughs beheaded by the explosions and now exposed in the precipitous caldera wall.

Front 20

Although there are no glaciers in Crater Lake National Park today, several geological features show that the area was glaciated in the past. List at least four lines of evidence for this past glaciation

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Exposed horizons of glacial debris, grooves of glacial stritations on the cliffs, large U-shaped calles on the south side of the park

Front 21

What evidence shows that there were multiple episodes of glacial advance and retreat during the Pleistocene Epoch?

Back 21

Moraines of many ages and types