Volcanic activity has occurred in Central Oregon for the past 40 million years, and will likely continue in the future. The volcanoes scattered throughout Central Oregon make up one of the most active and diverse sections of the entire Cascade range. Join geologist Daniele McKay to explore the history of these volcanoes, from explosive eruptions to quiet lava flows. We'll examine deposits left behind by ancient volcanoes, and consider what future volcanic activity in Central Oregon might look like.

1. Geology of Central Oregon’s Cascades
Deschutes Land Trust – Nature Nights Series
January 28, 2015
Daniele McKay
Oregon State University – Cascade Campus
John Williams

2. • Why are there volcanoes in central Oregon?
• Why are the Oregon Cascades composed of two
volcanic mountain ranges?
• A brief history of everyone’s favorite central
Oregon volcanoes.
Outline:

3. Subduction of the
Juan de Fuca Plate
beneath the North
American Plate:
Creates a linear
range of volcanoes
parallel to the
subduction zone.
Volcanoes in central Oregon:

4. The central Oregon
Cascades are the most
active section of the
Cascade Range.
Volcanoes in central Oregon:

5. 5-10 million years old
0-5 million years old
10-17 million years old
>17 million years old
The central Oregon
Cascades are the most
active section of the
Cascade Range.
They are also one of the
most active parts of
North America.
Volcanoes in central Oregon:

6. Why is central Oregon so active?
North and NW
trending faults
cut through SE
Oregon.
These faults
intersect the
Cascades in
central Oregon.
Faults provide
easy pathways
for magma to
reach the surface.

7. The Western Cascades:
older volcanic rocks
The High Cascades:
younger volcanic rocks
Volcanoes in central Oregon:

8. HIGH CASCADES
WESTERN CASCADES

9. High Cascades
~5 million years ago to present
Young,
active
volcanoes.
Very recent
lava flows,
ash deposits,
and cinder
cones.

10. Young,
active
volcanoes.
Very recent
lava flows,
ash deposits,
and cinder
cones.
High Cascades
~5 million years ago to present

11. John Williams
Young,
active
volcanoes.
Very recent
lava flows,
ash deposits,
and cinder
cones.
High Cascades
~5 million years ago to present

12. Western Cascades
~40 million years to ~5 million years old
No recent
volcanic
activity.
Old, eroded
volcanoes
that have
been extinct
for millions
of years.

13. Why are there two parallel volcanic ranges?
http://wordpress.up.edu/totle/cascadia-earthquakes-and-
tsunamis/cascadia-earthquakes-and-tsunamis-animations/
Plates don’t always
move as one unit.
Most plates consist of
individual “blocks” that
move at different
speeds and directions.

14. Rotation of Oregon:
Based on GPS
measurements.
Rotation is more
pronounced in western
Oregon and Washington.
10 mm/year
Permanent GPS Stations
GPS Surveys
McCaffrey et al., 2007
Why are there two parallel volcanic ranges?

15. Why are there two parallel volcanic ranges?
The Western Cascades have
rotated away from the
region where magma is
being produced.
The High Cascades are
located directly over the
region where magma is
produced, so this is the
active section of the range.

16. Where can we go to see the remains of
older Cascade volcanoes?
In central Oregon,
rocks exposed at
the surface are
very young.
To see older rocks,
we need to go to
places where
rivers and streams
have eroded
through the
younger rocks at
the surface.

17. In central Oregon,
rocks exposed at
the surface are
very young.
To see older rocks,
we need to go to
places where
rivers and streams
have eroded
through the
younger rocks at
the surface.
Whychus Canyon, Tyler Roemer
Where can we go to see the remains of
older Cascade volcanoes?

18. In central Oregon,
rocks exposed at
the surface are
very young.
To see older rocks,
we need to go to
places where
rivers and streams
have eroded
through the
younger rocks at
the surface.
Whychus Creek, Greg Burke
Where can we go to see the remains of
older Cascade volcanoes?

19. In central Oregon,
rocks exposed at
the surface are
very young.
To see older rocks,
we need to go to
places where
rivers and streams
have eroded
through the
younger rocks at
the surface.
Alder Springs
Where can we go to see the remains of
older Cascade volcanoes?

20. In central Oregon,
rocks exposed at
the surface are
very young.
To see older rocks,
we need to go to
places where
rivers and streams
have eroded
through the
younger rocks at
the surface.
Deschutes Canyon
Where can we go to see the remains of
older Cascade volcanoes?

21. After Kenneth A. Bevis © 2013
Late Miocene
Volcanic & Sedimentary Rocks
Western Cascades
Prior to 5 million years ago:
Deschutes Basin
Prior to ~5 million years ago, the Cascades produced volcanic deposits
that filled the Deschutes Basin.
Where can we go to see the remains of
older Cascade volcanoes?

22. After Kenneth A. Bevis © 2013
Late Miocene
Volcanic & Sedimentary Rocks
Western Cascades
~5 million years ago:
Deschutes Basin
Faults
Faults
Prior to ~5 million years ago, the Cascades produced volcanic deposits
that filled the Deschutes Basin.
~ 5 million years ago, north trending faults cut through the Cascades.
Where can we go to see the remains of
older Cascade volcanoes?

23. After Kenneth A. Bevis © 2013
Present day:
Deschutes Basin
High Cascades
Western Cascades
Prior to ~5 million years ago, the Cascades produced volcanic deposits
that filled the Deschutes Basin.
~ 5 million years ago, north trending faults cut through the Cascades.
The High Cascades are built inside the remains of older volcanoes.
Where can we go to see the remains of
older Cascade volcanoes?

24. Where did these faults come from?
Faults cutting
through SE
Oregon offset the
landscape:
Blocks that
dropped down
form basins.
Blocks that were
pushed up form
ranges.

25. Where did these faults come from?
Horst
(range)
Faults cutting
through SE
Oregon offset the
landscape:
Blocks that
dropped down
form basins.
Blocks that were
pushed up form
ranges.
Graben
(basin)

26. Where did these faults come from?
Horst
(range)
Faults cutting
through SE
Oregon offset the
landscape:
Blocks that
dropped down
form basins.
Blocks that were
pushed up form
ranges.
Graben
(basin)

27. After Kenneth A. Bevis © 2013
Deschutes Basin
High Cascades
Western Cascades
Where did these faults come from?
Faults propagating across SE Oregon have created basins and ranges.
~ 5 million years ago these faults intersected the Cascades, creating a
basin.
Since that time, the High Cascades have been built up inside the basin.

28. After Kenneth A. Bevis © 2013
Deschutes Basin
High Cascades
Western Cascades
Recent volcanic activity in central Oregon:

29. Recent volcanic activity in central Oregon:

30. 400,000 ybp
Oldest rocks:
Newberry Volcano
300,000 ybp
Oldest rocks:
Broken Top
120,000 ybp
Oldest rocks:
North Sister
50,000 ybp
Oldest rocks:
South Sister
48,000 ybp
Oldest rocks:
Middle Sister
12,000 ybp
Oldest rocks:
Mt. Bachelor
7,000 ybp
Lava Butte
1,300 ybp
Big
Obsidian
Flow
3,000 ybp
Santiam
Pass Flows
2,000 ybp
South Sister
32,000 ybp
Dogs domesticated
1,500 ybp
Fall of Rome
75,000 ybp
Modern
humans leave
Africa
200,000 ybp
First modern
humans
14,300 ybp
Paisley Caves
7,000 ybp
First beer
3,500 ybp
First use
of wheel
75,000 ybp
Newberry
Caldera
Recent volcanic activity in central Oregon:

31. Newberry
Volcano:
400,000 years
ago to present
Shield shaped,
has produced
highly explosive
eruptions of ash
and pumice, &
also effusive
lava flows.
Recent volcanic activity in central Oregon:

32. Newberry
Volcano:
400,000 years
ago to present
Shield shaped,
has produced
highly explosive
eruptions of ash
and pumice, &
also effusive
lava flows.
Sunset on Obsidian, Greg Burke
Recent volcanic activity in central Oregon:

33. Shield
Volcanoes:
Low profile,
gradual slopes.
Constructed of
hundreds of
layers of
overlapping
lava flows.
Types of volcanoes:

34. Strato –
volcanoes:
Tall and pointy,
steep slopes.
Constructed of
overlapping
layers of ash,
pumice, and
lava flows.
Types of volcanoes:

35. Cinder Cones:
Small cone
shaped
volcanoes,
steep slopes.
Constructed of
loose cinders
and lava flows
that emerge
from the base.
Types of volcanoes:

36. Types of volcanoes:
These classifications
are useful for
describing the shapes
of volcanoes.
They are not particularly
useful for describing the
eruption style of individual
volcanoes, or the complete
history of individual
volcanoes.

37. View from Newberry, J.M. Mestdagh
Newberry
Volcano:
400,000 years
ago to present
Shield shaped,
has produced
highly explosive
eruptions of ash
and pumice, &
also effusive
lava flows.
Recent volcanic activity in central Oregon:

38. Broken Top:
300,000 to
150,000 years
ago
Shield volcano
topped by a
stratovolcano.
Highly eroded
by glaciers.
John Williams
Recent volcanic activity in central Oregon:

39. North Sister:
120,000 to
50,000 years
ago
Mafic
stratovolcano.
Highly eroded
by glaciers.
Winter Sunrise, Kathy Lowery
Recent volcanic activity in central Oregon:

40. Middle Sister:
48,000 to
14,000 years
ago
Stratovolcano,
various
compositions.
Winter Sunrise, Kathy Lowery
Recent volcanic activity in central Oregon:

41. South Sister:
50,000 to
2,000 years
ago
Stratovolcano,
various
compositions.
What’s up with
the “bulge?”
Winter Sunrise, Kathy Lowery
Recent volcanic activity in central Oregon:

42. Mt. Bachelor:
12,000 to
8,000 years
ago
Shield volcano
topped by a
summit cone.
The “bulge”
Mount Bachelor, John Williams
(uplifted area)
extends to the north side of Mt. Bachelor.
Recent volcanic activity in central Oregon:

43. • Regional tectonics makes central Oregon one of
the most volcanically active places in North America.
• Rivers and streams in the Deschutes Basin have
exposed rocks from the ancient Western Cascades.
• Many of our favorite volcanoes are still active and
future activity is likely.
Conclusions:

44. Thank You!
Scout Camp Springs, Jim Davis