America's Volcanic Past -
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| "Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994 |
Volcanic Highlights and Features:
[This list is just a sample of
various North Dakota volcanic features or events and is by no means inclusive.]
North Dakota lies within the Interior Plains,
that vast region stretching from
the Rocky Mountains to the Appalachians. In North Dakota,
the Interior Plains are divided into
two major physiographic provinces by the Missouri Escarpment.
To the north and east of the escarpment lies the Central Lowlands Province,
characterized by its glacially smoothed landscape. To the south and west,
the Great Plains Province rises
gradually westward toward the Rocky Mountains.
White Butte, at 3,506 feet above sea level
in the southwestern corner of the state, is
the highest point in North Dakota. The lowest
point in the state is 750 feet above sea
level, where the Red River crosses into
Manitoba. At its most basic then, North Dakota
forms a gentle plain that slopes northeast.
But this surface is greatly modified by
landforms created by glacial ice, glacial lakes,
and catastrophic floods of glacial
meltwater, as well as by the relentless
erosion by water and wind that created the
buttes and badlands of the southwestern
part of the state. Through the eyes of a
geologist, the North Dakota landscape
is tremendously varied, ranging from
exceptionally flat plains of
glacial lakes to rugged badlands.
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The Interior Plains:3
North Dakota and the Interior Plains:1
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| Badlands |
North Dakota Badlands:2
About 60 million years ago, streams carried eroded
materials eastward from the young Rocky
Mountains and deposited them on a vast lowland --
today's Great Plains. During the warm, rainy periods
that followed, dense vegetation grew, fell into
swamp areas, and was later buried by new layers of
sediments. Eventually this plant material turned into
lignite coal. Some plantlife became petrified; today
considerable amounts of petrified wood are exposed
in the badlands.
Bentonite, the blue-gray layer of
clay, may be traced to ash from ancient volcanoes
far to the west.
But even as sediments were being
deposited, streams were starting to cut down through
the soft strata and to sculpt the
infinite variety of buttes, tablelands, and valleys
that made up the badlands we know
today.
Bentonite Clay:2
The story of the badlands begins over
65 million years ago during the Paleocene
Epoch. The dinosaurs had just become
extinct at the end of the Cretaceous
Period. The western half of North America
was buckling and folding to create the
Rocky Mountains. Large amounts of sediments
were forming as water, wind, and
freezing worked to break down the mountains.
These sediments, mostly sand, silt,
and mud, were carried off the eastern slopes
by ancient rivers and deposited here
in layers. Volcanoes in South Dakota,
Montana, Idaho, and across the west were
also erupting during this time, spitting
out huge amounts of ash. Some of this
volcanic ash was blown or carried by rivers
into North Dakota and accumulated
in standing water. Over time, the sediments
turned into the sandstone, siltstone,
and mudstone layers now exposed in the park,
while the ash layers became
bentonite clay.
| Killdeer Mountains |
Killdeer Mountains:1
The buttes that make up the
Killdeer Mountains are erosional outliers,
probably places where large lakes
in which sandy and limy sediments and
some stream deposits accumulated
in middle to late Cenozoic time.
Repeated volcanic eruptions in the
Rocky Mountains to the west produced
large amounts of ash, which blew eastward,
fell to the ground, and washed
into the lakes, forming tuffaceous
(meaning they contain volcanic ash)
sandstones. About 5 million years ago,
long after the lakes were filled, a new
erosional cycle began. The relatively
hard tuffs and freshwater limestones
and sandstones that had been deposited
in the Miocene lakes were much more resistant to erosion than were the surrounding
sediments. Because of their resistance to erosion,
these hard materials remained standing above the surrounding area as the
softer Golden Valley and Sentinel Butte
sediments were eroded and carried away by
streams and rivers to Hudson Bay. The
Killdeer Mountains, with their resistant caprock,
are the result of that erosion cycle;
they are the modern manifestation of an
ancient lake bed.
Arikaree Caprock:1
The Arikaree caprock of the Killdeer Mountains consists of tuffaceous
sandstone and siltstone
that is interbedded with thin layers of freshwater
carbonates. Dating techniques
performed a tuffaceous layer 200 feet
below the top of South Killdeer Mountain
indicated that volcanic ash at
that horizon was deposited approximately
25 million years ago. The
presence of interbedded carbonates
in the tuff would make mining and
processing of this material very difficult.
The tuffaceous rocks are present
throughout the 4,800 acre area of the Killdeer Mountains.
| Little Missouri Badlands |
Weathered Volcanic Ash Marker Beds:1
The most widespread and spectacular badlands in North Dakota border the Little Missouri River, northward from the headwaters area in Wyoming, where they are developed in rocks as old as Cretaceous, to the point where the river flows into the Missouri River. Some exposures in the northern part of the Little Missouri Badlands are eroded from beds as young as Eocene age, but most of the area of the badlands along the Little Missouri River is carved from the Bullion Creek and Sentinel Butte formations, both of Paleocene age. The sedimentary layers exposed in the Little Missouri Badlands are mainly continental sediments that were deposited by rivers and streams flowing east to the Dakotas from the Rocky Mountains in Montana and Wyoming at the time of the Laramide orogeny. They consist of layers of poorly lithified siltstone, claystone, sandstone, and lignite coal that were deposited in a coastal plain environment. River, floodplain, and swamp deposits predominate. Bluish gray layers of weathered volcanic ash form excellent marker beds in places and brownish gray layers of sand containing thin, orange, iron-rich bands also form prominent markers. Black veins of lignite coal are common and reddish bands of clinker (materials that were baked when buried lignite veins burned) add color to the area.
| Theodore Roosevelt National Park |
Theodore Roosevelt National Park:1
Theodore Roosevelt National Park consists of a North Unit, near Watford
City (McKenzie County) and a South Unit, near Medora (Billings County).
Between the two units, 70,228 acres (about 110 square miles)
of land are included in the park boundaries.
The badlands of Theodore Roosevelt National Park,
formed mainly through erosion by the Little Missouri River,
have attracted geological interest since the days
of the early scientific explorers primarily because of the well
exposed rock formations and the scenic beauty of the area.
Two primary rock formations are exposed in the
park, the Bullion Creek Formation and the overlying
Sentinel Butte Formation.
A widespread ash/bentonite deposit called Sentinel Butte ash, at
times 25 feet thick, occurs in the Sentinel Butte Formation in the
North Unit.
Sentinel Butte Bentonite:1
During the Laramide, volcanoes erupting to the west spewed ash that was carried by the wind to western North Dakota where it washed into wet areas - lakes and lagoons. With the passage of time the ash was transformed to bluish, bentonite clay layers that can be seen today in the badlands areas. Bentonite is composed principally of the clay mineral montmorillonite, which if it contains sodium as an exchangeable ion, can swell conspicuously when wet; calcium bentonites are only slightly swelling or non-swelling. The Sentinel Butte bentonite is an iron- and sodium-rich montmorillonite, one of three major Paleocene-age bentonites in North Dakota shown to have been derived from volcanic ash. The bentonites in the badlands can absorb up to several times their weight in water and they are extremely slick and mobile when wet. They form a characteristic popcorn-like surface when dry.
| Volcanic Ash and Tuffs |
Volcanic Ash and Tuffs:1
Several volcanic ash beds or tuffs are known
to be present in western and central North Dakota.
These tuffs range in age from 70 to 20
million years and are believed to have
originated from volcanoes in south-central and
western Montana and northern Wyoming.
Numerous additional volcanic ash beds are
likely present in the Pierre and Niobrara formations
but most, if not all, of the glass shards
have been altered to bentonitic clay.
These tuffs generally are thought to be the result
of single or related airfall events that likely
deposited a rather thin layer of volcanic dust
across a wide area. In turn this volcanic dust
was transported by wind and rain into streams
and redeposited in local basins, commonly lakes,
as thick tuffs. As a result of this reworking,
an inch or less of volcanic dust may result in
20 feet or more of tuff. The glass grains or shards
in tuffs have been used in the manufacture of road
base construction, concrete
admixtures and aggregates, abrasives, cleansers,
polishing compounds, slow release fertilizers,
ceramics, absorptives, and fillers.
Tuffs have been discovered in Emmons, Sioux, Stark,
Dunn, Slope, and McKenzie counties.
The most well known tuff deposit is the
Linton Ash which has been actively promoted for
a period of twenty years but has undergone little development.
Antelope Creek Ash:1
A 2-to 3 foot tuff layer (Antelope Creek Ash) is present in the lower
portion of the Brule Formation in the
Little Badlands southwest of
Dickinson.
This tuff is very fine grained
and initial attempts at dating this layer failed.
The Antelope Creek Ash
may extend over an area of 2000 acres.
Arikaree Caprock:1
The Arikaree caprock of the Killdeer Mountains consists of tuffaceous
sandstone and siltstone
that is interbedded with thin layers of freshwater
carbonates. Dating techniques
performed a tuffaceous layer 200 feet
below the top of South Killdeer Mountain
indicated that volcanic ash at
that horizon was deposited approximately
25 million years ago. The
presence of interbedded carbonates
in the tuff would make mining and
processing of this material very difficult.
The tuffaceous rocks are present
throughout the 4,800 acre area of the Killdeer Mountains.
Linton Ash:1
The Linton Ash is well exposed in the hills
north of the town of Linton in
Emmons County. The Linton Ash occurs
in the lower part of the Fox Hills
Formation and consists of 25 feet of
fine grained, moderately indurated
tuff. There is approximately 500
million tons of ash in a 4,000 acre area
around Linton.
Marmarth Ash:1
The Marmarth Ash, is present in the uppermost part of
the Hell Creek Formation northeast of
the town of Marmarth in Slope
County. The Marmarth Ash consists of
approximately 6 feet of unaltered
(white) tuff which is bounded by bentonite (gray).
The bentonite was
formed by the alteration of the volcanic glass.
This tuff could only be
traced through portions of two sections
indicating it may only extend over
an area of 600 acres.
Sentinel Butte Tuff:1
The Sentinel Butte tuff or blue bed occurs near the middle of the Sentinel
Butte Formation in McKenzie County.
The Sentinel Butte tuff is best
exposed in the North Unit of the
Theodore Roosevelt National Park and
extends to the northern edge of
McKenzie County, an area of at least 600
square miles.
The
Sentinel Butte tuff is up to
23 feet thick commonly comprised of an
unaltered tuff layer ranging
in thickness from 0 to 6 feet which is bounded
by bentonite layers that range up to 12 feet thick.
Excerpts from:
1) North Dakota Geological Survey Website, July 2001
2) U.S. National Park Service,
Theodore Roosevelt National Park Website,
2002
3) USGS/NPS Geology in the Parks Website, August 2001
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