BIO 220 W6 Discussion Question One
BIO 220 W6 Discussion Question One
Study the following articles:
.ehow.com/info_8259688_plants-animals-around-volcanoes.html”>http://www.ehow.com/info_8259688_plants-animals-around-volcanoes.html .nps.gov/sucr/naturescience/index.htm”>http://www.nps.gov/sucr/naturescience/index.htm
Based on the above articles and your understanding of ecosystems and populations from this course, explain how volcanoes both destroy and rejuvenate ecosystems. Make a prediction about how the succession of plants and animals will unfold as the landscape at Sunset Crater Monument recovers from the volcanic eruption. What are other geological risks that could have positive and negative impacts?
Volcanic eruptions are major natural disturbances with
varied and complex consequences. Recent studies of how
plants colonize newly created volcanic surfaces already
have begun to clarify our understanding of succession.
Because volcanoes create disturbance mosaics, it is
imperative that we more fully understand the biotic
responses. The 1883 eruption of Krakatau captured the
world’s imagination and initiated widespread and intensive
studies of succession following volcanic events (Docters
van Leeuwen, 1929). In this chapter, we review the state
of our knowledge of succession after volcanic events and
attempt to develop a general understanding of the
mechanisms that affect the development of volcanic
landscapes.
Volcanic eruptions punctuate the geological record and
human history. The Santorini, Greece, eruption (ca. BC
1470) probably destroyed Minoan civilization, and the
collapse of the Maya is attributed to climatic impacts
caused by eruptions of El Chichón in AD 900 and AD
1250 (Anonymous, 1993). Indirect volcanic effects also
destroy. When Iceland’s Laki fissure spawned the largest
volcanic episode in recorded history (AD 1783),
Icelanders starved, summer failed, and European markets
crashed (Gratten and Braysay, 1995). Despite monitoring
warnings, ash and mud flows from the Mount Pinatubo,
Philippines eruption in 1991 that killed 700 people,
displaced 500 000 villagers, closed a U. S. air base, and
eliminated 40 000 jobs. Ash veiled the planet and sulfuric
acid reduced the ozone layer thickness. Altered weather
patterns led to extreme floods of the Mississippi River
Valley in central U. S. A. (Tizon, 1996).
Volcanoes occur along tectonic plate margins and
within plates (Francis, 1993). There are currently about
550 active land volcanoes. Volcanoes associated with
ocean plates occur in the Maldives and Réunion in the
Indian Ocean, the Azores in the Atlantic, and Hawaii in
the Pacific. Continental plates once produced floods of
lava from fissures (e.g., the Indian Deccan plateau), but
today most active volcanoes are along plate margins.
Diverging plates spawn open-ocean volcanoes such as
Surtsey, Iceland, or rifts, as in East Africa. Converging
plates spawn huge earthquakes and volcanism, such as
routinely occur along the Pacific Basin Ring of Fire.
This chapter describes typical volcanic disturbance
regimes and their ecological consequences. How does the
biota respond to these impacts? We will emphasize
disturbance regimes, recovery mechanisms, and recovery
rates.
VOLCANIC IMPACTS
New volcanic surfaces are created by lava, pyroclastic
flows and air-borne deposits (tephra), debris flows, lahars,
and avalanches (See Table 1 for definitions). Primary
succession is associated with lavas, pyroclastic flows, and
most lahars, but may occur on any material. Secondary
succession occurs most frequently on thin tephra and some
lahars because some biota or soil may survive (Halpern et
al., 1990; Grishin et al., 1996). Volcanic gases create
strong, but local, impacts. Once the gases subside,
primary succession usually results, modified by the nature
of the substrate in question (Fig. 1). Climate, substrate
type, and landscape factors all affect the recovery rate.
Volcanism is associated with earthquake zones, being
produced by the same fundamental forces. Tsunamis are a
consequence of both.
These sea waves are usually
spawned by coastal earthquakes, but a devastating tsunami
resulted from the collapse of the Rakata cone of Krakatau
(1883) and killed more humans than the eruption itself
(Francis, 1993). The effects of earthquakes and tsunamis
on an ecosystem may be ephemeral or persistent. Space
does not permit a review of these effects here, but the
consequences share much with the principles developed in
this chapter.
Lava
Lavas cover much of the earth, but recent large flows
are rare. Lavas are viscous and flow slowly—thus they
are the least dangerous volcanic event. Molten lavas may
ooze from fissures, vents, hot spots (e.g., Réunion and
Hawaii), and rifts (e.g., East Africa) to form new land. For
ecological purposes, lavas can be divided into those
forming a mass of small, loose, irregularly shaped blocks
(known by the Hawaiian term a’a), smooth, ropy lavas
(known by the Hawaiian term pahoehoe), large angular
blocks, and domes found within craters.