Volcanic Landforms
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Key Concepts
• ~t landform< do
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• How
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• Wl'wl ott- dntincti~ features
occur in .... leani< ...... ?
Key Terms
• 1hi4!1d YOlar>o • onder ~
•
•
•
•
composite 'I'OIcaoo • U11doer.
vol,..nic M'Ck • dike
sill • ~thoIith
geotlletmll ICtJVJtY • ~
~ Target R_ding Skill
Outllnlnt As you fNd. "....,,. ...
outline.tlout wkMlil: WodfooiliS
th.It )'OU c.n oM for rewieow. Use the
red hudirogs fOf main topics arod
the blue he~ fof subtopla.
L Landf....... from IIH -.d Ash
A. ShIt'ld
Vol<.a.-s
••
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o.
How Can Volcanic Activity
Change Earth's Surface?
1. (he tape to secure the nedt of /I
one end of iI slr_.
2. ~,. the balloon in the center of
• bo;c ""fith the straw Ilfotruding.
3. Partially infl.t,. the balloon.
balloon
0Yfi
... Put damp sand on top of the balloon until it is <ownd.
s. Slowly inflate the bililoon more. Observe what holppem
to the SUnK,. of the sand.
Think It Oftr
~king MoOeb This.aMty models one of the w;tyl' in which
YOluonic Ktivity yn Uluse II mounUlin to form.. wtwot do)'OU
think the sand ,eptestnU1 wtwot does the balloon reprewnH
Volcanoes have created some of Earth's mos( spectaeular land­
forms. ~ perfect COIN' of Mount Fuji in Japan. shown in
Figure I), is famous around the world..
For much of Earth's hiMory, volcanic activity on and
beneath the surface has buill up Earth's land areas. Volcanic
activily also formed the rock of Ihe ocean floor. Some VQlcanic
landforms ari.$e when lava flows build up mounlains and pla­
teaus on Earth's surface. Other volcanic landfornu are Ihe
result of Ihe buildup of magma beneath lhe surface.
L
II. Uo'oltforms from ~ ....
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Mount FuJI
The .JITlOJI ~ vok¥1i( u,...•
of Mount Fuji in DpMl has long
been. t.,.orite subject lor 1Irma.
.
, "
Landforms From Lava and Ash
Volcanic eruptions creal~ landforms made of lava. ash, and
other matnials. These landforms include shield wlc:anoes.
cindcTCOM \'Ok:anocs, composite rokanocs,and lava plateaus.
look at Figure 14 to see these features. ADothcT landform results
from the collapsl:' of a volcanic mounlain.
Shield Volcanoes AI some places on Earth's surfKr. thin
layers of lava pour out of a ~t and harden on lOP of pr~us
layn-s. Such lava flows gradually build a wide, gently sloping
mounlain c:aJltd a shiilCl VOIOlQO. Shield \'Olcanoes rising from
a hoi spot on the ocean floor created the Hawaiian Islands.
Cinder Cone Volcanoes If a volcano's lava has high viscos­
ity, it may produce ash, cinders. and bombs. ThCSl: materials
build up around the \~nt in a steep, cone-shaped hiJI or unall
mountain called a cinder cone. For example. ParkUlin in
Maico erupted in 1943 in a farmer's cornfield. The volcano
built up a cinder cone about 400 melers high.
ftGuR~
14
Volcanic Mountains
Voluonic: Ktivity iI r.-.pomiblt!' for
building up mudI of Earth's
wrlKll.l..noa from vok..I~ cooI5
and ~rdMl; Into three type'! of
mounlillM. It U10 abo form levil
~tuus. o.utfy;ng W1Y1 ~
of IIOIano is forn1ed frgm lhil\
Jow.sihu '-"
Composite Volcanoes Somt1imes, lava flows alternale
with aplOSM auptions of ash, cinder, and bombs. lbe resull
is a composite volcano. [Composite volcanMi are tall, cone­
shapnf mountains in which layers of lava ahernate with layers
of ash. Examplesof composile volcanoes include Mounl Fuji in
Japan and Mounl St. Helens in Washinglon Stale.
Lava Plateaus Inslead of forming mountains. some erup­
tions of lava form high, level areas called lava plateaus. Firsl.
lava flows oul of several long cracks in an area. The thin. runny
lava travels far bdore cooling and solidifying. Again and again.
floods of lava flow on lOp of earlier noods. After millions of
years, these layers of lava can form high plateaus.. One example
i5 the Columbia Plateau. which covers paris of Ihe states of
Washinglon, Oregon, and Idaho.
Shldd Volaono
Quiel eruptic:>nl; gradually build
up a gently 510ping maunUin.
151i1nd of HilwiI,i
--­
Onder Cone Voluono
Ash. anden, ¥'CI bon>b5
erupt oploWe+y to form
iI «N'lHhilped hill.
-
...
, ",
H_ ;) CioIdel'a Forms
Today, Crat~ l.1ke (right) fills an
almost
c.~;a. A c.~l1
forms ~ I vobno", magma
chitmbef empties i<>d the roof 01
em.....
the thilmbf<
(oll/l~
Calderas The huge: hole left by the collapse of a vola­
nie mounu:in is called a cakkn (ltal DAiR uh). The hole
is filled with the pieces of the vokano mat have fallen
inward, as well as some lava and ash.
o
The lop of II comp(>loit" .....1'10
exp!oda. l.1va flows partially empty
tM ""'9rM m.mber.
o
The foof of the ~ <;hamber
coilaploeS, fOfming;) uldefa.
How does a cakkn form~ Enormous eruptions may
empty the main vent and the magma chamber Ixnealh a
volcano. ~ mountain becomes a hollow shell. With
nothing to support it, the lOp of the mountain collapses
inward, fonning a caldera.
In Figure- 15 you can set steps in the formation of Cra­
ter lake, a caJdera in Ortgon. Crater I..akco forrTled about
7,700 ynrs ago whrn a huge explosive uuption partly
emptied the magma chamber of a YOkano called Mount
Mazama. When the YOICino exploded, the lOp of the
mountain 1'1'35 bIastnj inlO the a~_ 1'ht caklera
th.iJ.t fonned eventually filled with water from rain md
snow. Wizard Island in Craler Lakt is a small cinder cone
that formed during a later r'fUpOon inside the caldera.
Soils From Lav••nd Ash Why would anyone live
nur an aaive \'Okano? People often stttk dose to volca­
noes to Iakc adY.lntagc of the fertile vokanM: soil The
o
l.1tef. a small cinder tone
lonns In the uldefa. wtoidl
~ fil.. Mtto wile!".
102 • F
lava, asb, and cinders thaI erupl from a volcano art ini­
lially barren. Over time, however, the hard surface of the
lava bn"ab down to form soil. Whm YOIcanic ash breaks
down, it rclC<ll;CS potassium, phosphorus, and other sub­
slaoces thaI plants n«d./u soil develop$. plants are able
to grow. Some volcanic soils an: among the ridlcsl soils
in the world. Saying that soil is rich means that iI'S fertile,
or able 10 suppon plant growth.
Landforms From Magma
Somc1.imn magma forces its ~y through cncb in the upper
crust, bm fails 10 ICICb. the surface. There the magn'UI cools and
twdens inlO rock. ()yn time, the forca Nt W\'af .""'y brth's
wrf.ace.-5ucb as Rowing WOlIn. icc, Of wind--JNy strip IIW3Y
tM byus abo¥t the lwdcDcd .mpna and fuWly erpoK it.
Fntum: formed by magma indude Wllcanic nc<b, dikes.
and sills. as wdI as bathotiths and dollK mountains.
Goenline
- 5I:i,~~g ~
(
f«: u.b llII"*- .etaI.
\/bit
==
'itil inb "'9
WitlI tMoI: -.llBt
VokAnk Necks A wIcanic ned )gob lib a giant tooth
Ad in the pound. A jijl(jrik Mat forms when magma hard­
ens in I vokano'. pipe. Tht toItc:r rock around the pi~ wellS
away. cxpoeins the hard rod of the l'Okanic ned. Ship Rod in
New Mcrim, shown in Figun' 16, i5 I \'Ok:an.ic ned forIDl:d
(rom I YOkano INiI nuptcd about 30 million)Uf'5 ago.
Dilles .nd Sills Magnu that forccs iudf ~ rock layn-s
hardnu into a diU. Sormtirnes. a diU an Ix seen slanting
through bedrock ...tong a highway 0It.
Whtn magma squeezes 1M:t~ horizontallayen of rod, it
forms a mt. One famous c:nmple of a sill is the p,j~des in
New York State and New Je:rsq. The Palisades form a series of
long, dark cliffs. These cliffs SUtt(h for about J() kilometers
<IIon8 Ihe west ~ of the Hudson Rivtt.
..... "
VoUnk HecU. 00tes, WId Sills
Magma tn.t '-denl benuth tM
wrlKt ~ fOl'm 'IOIanlc: neda.
dilr.M, and sills. '" dike tlltench
outw¥CI from Ship Rock., •
......,;c ned: in N_ Muico.
w,....il.Mdc...baoU. WPYt
it the di~ wn<l~ I .. djh
MId;l Ill/l
Batholiths Llrge IlXk ffiasst'$ calI~ batholiths form the (ort
of many mountain ranges. A batholith (BATH UH lith) is a mass
of rock fonned whm a \alp' body of IIliIIgrnil cools inside I~
crust. The map in Figure 17 shows just how big batholiths really
are. The pholOgraph shows how iI batholith looks when the lay­
ers of rock above it have ...'Om away.
­...
• ••
•••
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Dome Mount41ins Other, smaller bodies of harden cd magma
can create dome mountains. A dome mounlain forms whom
uplift pushes il balhol.ilh or smaUer body of hardened magma
toward the surface. The hardened magma fom':5 the b~ of
rock to bend upward into a dome $hape. EventuaUy, the rock
aIxm: the dome mountain wears away. leaving it exposed. This
,.".",
procc:ss formed the Black Hills in South DUou.
SeYer. IMge ~tholiths form
Geothermal Activity
core of mountain ranges In
_em North AIneriu. Half
Dome In Yosemite tutioNl Pilr\.
c.lit~ is part of the ~ra
NroMia batholith.
~
The word gtOthnmlli comes from the Greek geo meaning
-Eanh- and tllnme meaning -heat.- In jeotbn'malldivity.
magma il f~ kilomctn1 ~eath Earth's $urfau heats under­
ground waler. A variny of geothermal featufa occur in volca­
nic areas. Hot springs and geysen are types of gcothcnnal
activily thai arle oftieR found in aras of pr«c:nl or past
,"OIc:anic activil}'.
Hot Springs A hot spring forms when groundwater is hnted
by a nearby body of magma or by hot rock deep underground.
The hot water rises to !he surface and coUects in a natural pool.
(Groundwater is water that has seeped into the spaces among
rocks dcrp beneath Eanh's 5Urfau.) Water from hot springs
may contain dissolved gases and other substances from deep
within Earth.
104 • f
Geysers Sometinxs, ri5ing kot water and steam become
trapped underground in a narl'(lW erxk. Pressure builds until the
mixture suddenly $prays above the surface as a geyser. A geyser
(CY lur) is a founlain of water and steam that erupts from the
ground. Figure 18 shows one of Earth's most famous geysers.
Geotherm~1
Energy In some volGlnic areas. water ~,lIed
by magma GIn provide an enC'TgY source Gllkd grotoomal
mergy. The propk of Reykjavik, [eeland, pipt this hot water into
homes for warmth. Grothermal energy GIn also bt used as a
source of electricity. Steam from underground is piped into tur­
bines. Inside a turbine, the steam spins a wheel in the 5artl(' w.Y
that blowing on a pinwheel makes the pinwheel turn. The mov­
ing wheel in the tumine turns a generator that change.; the
cncrgy of motion into dcctrica.l Oltt'gy. Geothermal energy pro­
video; some electrical power in California and New Zealand.
'!"';;;';!!~.~.,,;)
How ~n ~~I eMrg)" be uwd to
S'
~ . 01. !JeMI'"ate elKtridtyl
..... "
A Geysef Erupts
Old fllithful, .. ge)'\Itf in Yellowstone NoltionlII
PIIrk,
@/'Uptsabout eYer)" 33 to 93 m;nut~
That~
how long it take for the ~ e to
build up agiOin a~ "ach ~
Sect;on
4 Assessment
3, a. listing What are $Orne featurts found in
4@Target Reading Skill Outlining lM the infor­
aRali of grothcrma.i activity!
mation in your oullinC'lIbout vola.nic bndfonns to
b. Rfiating c.use kid EffKt Whal D.US<"$ a
hdp you aIlSWtt the questi0n5 bdow.
gqKr to erupt!
Reviewing Key Concepts
1... identifying What ue the thrtt main types of
vokanonr
b. CO!Ilpw;r,g" Contr.wtlg Compare the
thrtt ty~ of volanic mountains in term~ of
d1ape, lylX' oferuption, and the materials thai
mau up the 'IOlano.
2. iI. Listing Whal fealures form as a rtSult of
magnu. h2rd.ming btnealh Elrth's surface?
b. ~ What are two ways in which
mounUliru ClIl form as a result of magma
hardrninglxnC'alh Earth's surface?
L Predicting After millions of years, wNt
landform forms lTom homkned magma in the
pipe of an atinct voka~
Writing in Science
Ek22,' • • • ',
wnt. .. ~
of the piOCtiS tNt foI".ed er.... Lake. In
)"OU,
er, incLude the type of vokMait
~ n MIt aruption ia'MlMd. M M!I M
the . . in the proceB. (Hjnt Loot M the
dlagrMlIn Agan 15 brful.)"OU Wftle.)
.nsu.
Oa.epter 3 f . 105