Smithsonian Institution
Global Volcanism Network Bulletin v. 20, no. 2, February 1995
Fernandina (Galapagos Islands) Flank eruption slows but continues
until at least 19 March
Fernandina
Galapagos Islands, Ecuador
0.37S, 91.55W; summit elev. 1,495 m
All times are local (= GMT - 6 hours)
The fissure eruption first observed on 25 January (Bulletin v. 20,
no. 1), has continued sending lava flows down the SW flank and into
the sea. All of the new flows appeared to be aa lavas (figure 11).
Godfrey Merlen compared the eruption intensity in late January to
5 March and concluded that it had decreased significantly.
According to reports at press time, eruptions continued through at
least 19 March.
Tui De Roy was on the island during 8-16 February and part of her
report follows (the term "kipuka" refers to an area of older rocks
surrounded by younger lava flows). She saw two vent areas (figure
11): 1) an early eruptive site (active before she arrived) in the
crater of an old cone ("Old Cone"), and 2) a main vent where the
sustained activity that she witnessed took place ("Main vent"). She
also had a reconnaissance view of some small finger-like lava flows
at higher elevation ("inexact" on figure 11 and discussed below
under Early Activity).
"All of the activity has taken place along a prominently marked,
prehistoric radial fissure running from about half way up the
volcano right down to the shore. This fissure is marked by numerous
old cones of varying ages, ranging from a very old, elongated (and
perfectly aligned) well-vegetated cones covered in ancient ash at
the edge of a kipuka ["Old Cone"], to a string of 6-8 very recent
looking cones on the lower flats coming right down to the shore
[figure 11]. Significantly, a couple of very small new spatter
cones had been active briefly early in this eruption within the
crater of the old cone . . . . The entire length of this radial
fissure had built up through previous eruptions something of a
ridgeline down the flank of the volcano, which served to deflect
most of the current lava to its northern watershed, although later
in our stay an increasing number of flows were beginning to spill
over through a gap to the S, posing an imminent threat to the
wildlife oasis of Cape Hammond . . . ."
De Roy also noted that in many cases the paths of lava flows
descending the flank "could not be readily followed because of
undulations in the land and the fact that many of the flows
disappeared into lava tubes at several points." But, she did
describe flows that were visible, as follows.
"Both the active flows, as well as some that appeared to have now
stopped, meandered and braided down the slope, with arms
crisscrossing through irregular-shaped kipukas far to the NW of the
main and most direct path to the sea. A new flow (as shown on
Godfrey's map) reached the sea S of the main flows at about 0800 on
8 February where it formed a new delta and continued to advance
steadily before halting a couple of days later."
Although there were slight variations, the intensity and height of
the fountaining remained "remarkably steady" during her stay. The
single active main vent displayed continuous fountaining 50-100 m
tall. Fountains shot up both vertically and at oblique angles on
either side of the vent. During 8-16 February the spatter cone
around the vent grew considerably broader, but little taller. She
camped near the vent on 9 and 13 February (figure 11) and watched
the growth of a very blocky mass of rubble at the E base of the
cone.
The migration of flows toward the N is emphasized by comparing De
Roy's 16 February annotations of lava extent to the map completed
by Merlen about a week earlier (figure 11). Starting about 12
February new flow paths developed high on the slope. Some lava
flowed N as small fingers, but beginning at about 1600 on 12
February a large lobe flowed more southward than before. This
migration of lava flows to the N and S corresponded with a
progressive decrease in lava flow rate at the ocean entry (even
though, as previously mentioned, the fountaining at the vent showed
no marked decrease). By the time De Roy departed at noon on 16
February ". . . there seemed to be no more flowing of lava into the
sea, with only slight wisps of steam still rising along the shore."
On the nights of 13-15 February the glow from lava on the flats 1-2
km inland seemed to increase.
Although De Roy's observation of smoke and other airborne material
was from upwind positions, she reported the following: "Only a very
small amount of solid airborne particles appear to have been
emitted during the initial stage of the eruption. A minimal amount
of Pele's hair was evident near the shore, barely increasing in
density closer to the vent. Within 1-2 km of the vent a thin
dusting of light, gassy scoria littered the ground as in all
previously observed Fernandina eruptions, but in much lower amount
than some of the caldera eruptions of the 1970s and 1980s. Such
scoria was still being produced at the time of our visit, with
constant fallout in the area of our camp of 9 February whenever the
eruption cloud drifted above us. No signs of ash from this eruption
were present anywhere; although I did hear comment of `ash' dusting
one of the early boats to visit the site.
"Intense heat was rising from the main vent, with only moderate
amounts of bluish-white smoke. It rose vertically into a constantly
contorting, billowing, major thermal head, resembling a
thunderhead. In addition, a pall of amber-colored fumes surrounded
this cloud column and spread westward at all times, regardless of
the shifting directions of the wind at lower elevations, which
caused the main cloud to waver in various directions at different
times of day or night. This pall was particularly evident when
traversed by sunshine or moonshine, which took on a brownish hue.
This plume should have been evident on satellite images, regardless
of the main cloud possibly being mistaken for the normal
thunderhead prevalent over the island during this El Nino season.
The `smoke' from the vent did seem to increase very gradually
during our stay."
Besides the main vent, the eruption also produced voluminous
amounts of gases from two other sources: 1) several areas of the
main lava flow ~2 km below the main vent where degassing took place
at the mouths of lava tubes, and 2) at the lava's ocean entry where
mainly steam was rising. The first source of gases came out of the
main lava flow and was thought to be degassing at the mouths of
lava tubes.
Weather satellites (and shuttle astronauts) monitoring the
Galapagos vicinity have thus far been unable to obtain clear views
of the eruption plume. The difficulty has been screening from high
clouds coupled with inadequate eruptive plume heights. The TOMS
instrument that has successfully imaged Galapagos eruptions since
1979 failed in December 1994.
Having seen the eruption in late-January, Godfrey Merlen returned
to Fernandina on the night of 5 March and noted a reduction in the
comparative intensity of the eruption. In March the molten lava at
the ocean entry was "dripping rather than flowing." Though less
intense than in February, lava outflows remained concentrated at
the site where lava had initially entered the sea in January; in
March this amounted to about 10 separate outpourings over a 90-m
lateral distance. Merlen noted that the small delta created there
was about 5-m high and already cut back by waves forming an almost
vertical cliff face. In contrast to earlier stages of the eruption,
floating dead fish and the abundant wildlife feeding on them were
largely absent. In March the sea surface temperature was up to 45
deg C, while it was about 24.5 deg C at a distance from the new
delta. These temperatures were down from those in mid-February when
at equivalent spots temperatures were >60 deg C and about 27 deg C
(table 1). No new lava flows had moved to the S. Though still very
hot, the new flow appeared to have left nearby vegetation nearly
green, suggesting it may have been cooler when erupted than some of
the earlier lavas. Scoria thickness on the new cone's upwind base
averaged 5 cm.
Early Activity. Reports by De Roy, Merlen, and Day added
information on the eruption's earliest days before observers
arrived. The most notable signs were several small lava flows from
fissure vents high on the shoulder of the volcano (figure 11).
Viewed from a distance, these small flows appeared devoid of cones
or extensive accumulated lava.
As previously mentioned, the "old cone" (figure 11) contained two
or three early vents within its crater. These vents were marked by
steep black spatter. The spatter had been flung 20-30 m, coating
and charring trees. Those trees closest to the vents (located ~15
m from them) had their bark steamed off and were deep orange in
color. Although these vents were only briefly active, they
discharged a very rough aa flow.
Around the old cone many of the larger trees (Palo Santo and
Opuntia cacti) had lost limbs or been knocked down (uprooted or
snapped off at mid-height). The trees had predominantly fallen in
a downhill direction, radiating roughly away from the main vent. An
absence of directional scouring from scoria, and the presence of
Waltheria bushes repeatedly twisted around their bases, suggested
violent multidirectional wind gusts (a "tornado") rather than a
well-defined unidirectional blast. Within a kilometer of the vent,
however, Jasminocercus cacti consistently showed mild blistering
from excess heat on their ventward sides.
Merlen noted that during the eruption lightning and heavy rain were
commonly seen. For example, on the night of 28 January (prior to
the release of ponded lava into the sea at about 2230) there was
considerable sheet lightning coming from high clouds. Merlen also
noted that high columns of thick white steam rose on occasion to
approximately 4 km. The ascent of these plumes appeared dependant
on the flux of lava into the sea.
Submarine acoustic recordings were also made by Merlen on 27-29
January using a Benthos hydrophone. The recordings detected
extremely loud, echoing explosions at least 7 km from the lava's
ocean entry. These sounds were not heard during subsequent visits
(on 6-7 and 10 February); however, during all visits the
hydrophones received a cacophony of hissings, poppings, and
low-level thumps.
Some of Merlen's oceanographic observations are summarized in table
1. Within the discolored water Merlen also noted a ~100-m-diameter
circular patch of upwelling water that was "glassy-smooth" and
encircled by standing waves up to a meter in height on its margins.
Located near the shore and not shifting in position, the upwelling
water was cool and sufficiently turbulent to make steerage of the
dingy difficult. In contrast to the cool (19.6 deg C) upwelling
water, only 2-3 m away from its margin very hot (50 deg C) water
was found. The upwelling water was brought to his attention by
seabirds attracted to it. "Around this dramatic phenomenon and
spreading out from it were a quantity of dead fish representing a
mesopelagic fauna, including hatchet fish (Argyopelecus sp.), what
appears to be a scabbard fish (Aphanopus sp.), and others that have
yet to be identified." Although a limited amount is known about the
vertical ranges of these kinds of fish, their presence at the
surface may help determine the sources of this cold upwelling
water.
Biological Impact. De Roy noted that the wildlife appeared unable
to comprehend the dangers from the intense heat of the lava. Marine
iguanas were attracted to the warmth of active flows, climbed onto
them, and were ignited before being able to escape. On the other
hand, sea turtles and adult fur seals cruised through steaming
waters within meters of the lava flow edge and showed no immediate
signs of discomfort or injury. In other cases, it was unclear if
the water temperature or chemistry was more critical in causing
death (eg. pelicans, marine invertebrates, moray eels, and fish).
In the sea and along the shore, many animals were attracted by the
abundance of dead marine life floating on the surface. These
opportunistic species included frigate birds, boobies, brown
noddies, storm petrels, and many hundreds of pelicans. Merlen
mentioned pelicans with pouches scalded from diving into hot
seawater. In addition, De Roy saw sharks, sea lions, and flightless
cormorants feeding. The eruption also killed some land iguanas. If
lava flows were to reach Cape Hammond this would threaten
flightless cormorants, penguins, and marine iguanas as well as one
of the largest breeding populations of Galapagos fur seals. Merlen
closed his 28 February report with the words: "the overall
impression was that of biology in confusion."
Information Contacts: Tui De Roy, Patons Rock Beach, Takaka, Golden
Bay, New Zealand; Godfrey Merlen, skipper of motor vessel "Ratty,"
and David Day, Fundacion Charles Darwin Para Las Islas Galapagos,
Estacion Cientifica Charles Darwin, Isla Santa Cruz, Ecuador
(Email: dday@fcdarwin.org.ec); Full reports by Merlen and Day are
available on the Charles Darwin Research Station World Wide Web
site (URL http://fcdarwin.org.ec/welcome.html); Jim Lynch, Synoptic
Analysis Branch (see Barren Island); Cindy Evans, Lockheed (see
Barren Island).
Figure 11. SW Fernandina Island sketch map from an original ~9
February map by Godfrey Merlen with later annotations by Tui De
Roy. GPS points A, B, and C were recorded on 7 March. Point A lay
at the extreme S end of a new 80-m-wide aa flow that also passed
through point B. Point C lay at the foot of the S side of an active
cone.
Table 1. A summary of measurements and remarks comparing offshore
seawater and nearshore turgid water close to the lava's ocean entry
for the vigorous part of the eruption (late January and early
February). Courtesy of Godfrey Merlen.
Color Temp Secci disk visible Remarks
to (depth)
"Normal" water dark blue 27 deg C ~12 m --
offshore
Turgid water at bright green 31 deg C <2 m Up to ~2
from the lava's km offshore
ocean entry & extending
S of Cape
Hammond
landing
Adjacent the brownish-yellow >60 deg C -- Steaming
lava entry with rising
bubbles