Extrusive Activity

Question 1

(1) where does the cascade mountain range lie?

Answer 1

Along the western coast of the US extending from Northern California, through Oregon and Washington into British Columbia, Canada.

Question 2

(1) what is the cascade mountain range?

Answer 2

A continental mountain arc formed due to the subduction of an offshore oceanic plate (Juan de Fuca) beneath the continental crust (North American plate).

Question 3

(2) lava plateaux - when did the Columbia river lava plateaux form?

Answer 3

12-17 million years ago

Question 4

(2) lava plateaux - how big is the Columbia river lava plateaux?

Answer 4

It is regional in scale and covers 130,000 Km squared of the states of Washington and Oregon

Question 5

(2) lava plateaux - what did a fissure eruption result in?

Answer 5

Hundreds of separate effusive basalt flows - reach total thickness of 2000m

Question 6

(2) lava plateaux - what are basalt lavas?

Answer 6

Very ‘runny’ and take a long time to cool

Question 7

(2) lava plateaux - what is the form of volcanism in areas within plates associated with?

Answer 7

Mantle plumes or hot spots

Question 8

(2) lava plateaux - the plateaux is…….

Answer 8

Very distinctive and remains stable as a landscape over time

However it is gradually denuded and sculpted by erosion from wind, rain and rivers which incise into the plateaux

Question 9

(3) shield volcanoes - what are shield volcanoes made of?

Answer 9

Also made of fluid lava flows however unlike fissure eruptions the effusive lava erupts from a central vent, flowing in all directions.

Question 10

(3) shield volcanoes - there are various shield volcanoes along the cascade range, what do these include?

Answer 10

Belknap,
three fingered jack,
Mount Washington,
Mount bachelor

Question 11

(3) shield volcanoes - what does Belknap shield volcano and its surrounding lava flows cover?

Answer 11

98 sq. kilometres

Question 12

(3) shield volcanoes - when did Belknaps explosive phase begin?

Answer 12

Over 2900 years ago

Question 13

(3) shield volcanoes - Belknap is one of the cascades what?

Answer 13

Youngest volcanoes with lava flows as young as 1,400 years

Therefore is a dynamic landscape with potential to be rescaled in future as it receives fresh flows of lava from the central vent

Question 14

(4) cinder cones - how do cinder cones form?

Answer 14

From the build up of pyroclastic materials ejected from a single vent

Question 15

(4) cinder cones - what are cinder cones!

Answer 15

Explosive and geologically younger features which often from on the flanks of larger volcanoes

Question 16

(4) cinder cones - describe lava butte cinder cone in Oregon

Answer 16

It rises 500ft above the ground and has view over the cascade range. It formed 7000 years ago covering 9 miles with lava.

Question 17

(4) cinder cones - what is wizard islands?

Answer 17

A small cinder cone formed more recently which rises out of the lake that now occupies the crate lake caldera

Question 18

(5) calderas - what is crater lake caldera?

Answer 18

An example of a large caldera crater more recently filled with water

Question 19

(5) calderas - when did crater lake caldera form?

Answer 19

Around 6000 years ago

It is the remnant of a high volcano called Mount Mazama which lost its top as the lava beneath the mountain drained out in violent explosions and the top collapsed inwards.

Question 20

(5) calderas - what are calderas often distinctively characterised by?

Answer 20

Geothermal activity such as geysers and secondary features such as hot springs and earthquakes are often common

Question 21

(5) calderas - where is Yellowstone national park, Wyoming, situated?

Answer 21

Within a caldera, accounting for its many geothermal features.
Seismic unrest in the park has recently been detected which could indicate a period of further activity.

Question 22

(5) calderas - calderas are very large in scale, what does this mean?

Answer 22

They are less distinctive from the ground but more easily viewed by satellite.

Question 23

(6) stratovolcanoes and lava domes - what are stratovolcanoes?

Answer 23

Extrusive landforms often related to explosive volcanic activity at subduction zones

Question 24

(6) stratovolcanoes and lava domes - what are stratovolcanoes often characterised by?

Answer 24

A conduit system with a crater at the summit containing a central vent bringing magma up to the surface from a chamber below

Question 25

(6) stratovolcanoes and lava domes - where do parasitic cones often form?

Answer 25

On the flanks of composite volcanoes where lava may flow from fissures. Strengthening of the cone may occur when magma solidifies in dykes (vertical intrusions cutting across bedding planes)

Question 26

(6) stratovolcanoes and lava domes - Mount St. Helens volcano is.....

Answer 26

40,000 years old, 2549m high and still potentially active today Remained dormant from 1857-1980

Question 27

(6) stratovolcanoes and lava domes - during the five month period following the 1980 Mount St. Helens eruption what happened?

Answer 27

There were 5 small explosive eruptions which along with 16 small eruptions in 1986 created a lava dome in the crater formed in the 1980 eruption

Question 28

(6) stratovolcanoes and lava domes - what did the lava dome do to Mount St. Helens?

Answer 28

Plugged the vent and trapped gases leading to the build up of pressure and a subsequent explosive eruption shattering the dome and transforming the landscape.

Question 29

(7) EVALUATION - what is the cascade range?

Answer 29

A distinctive landscape produced by volcanic and seismic activity at an active subduction zone

Question 30

(7) EVALUATION - what is the cascade range a result of?

Answer 30

Activity that started 16 million years ago but has been shaped by subsequent activity up to the present day.

Question 31

(7) EVALUATION - some features of extrusive landscapes have the potential to what?

Answer 31

Change dramatically and periodically after millions of years of being shaped by denudation.

Question 32

(7) EVALUATION - the 1980 Mount St. Helens eruption triggered what?

Answer 32

The collapse of the North side of the volcano which brought secondary effects such as a land slide, superheated pyroclastic debris flows and Lahars.

Question 33

(7) EVALUATION - other landforms appear what?

Answer 33

Less dynamic e.g. Belknap shield volcano, but still have the potential to be shaped by the future tectonic activity

Question 34

(7) EVALUATION - lava plateaux in e range however are what?

Answer 34

Stable features which erode slowly over long periods of geological time.