April 13, 2000
We are in Mrs. Hood’s kindergarten
class studying the ocean. We just went on a pretend dive in
Alvin with Sarah Little and we have some questions.
- What kind of animals are down there?
- Do you ever see active volcanoes?
- Have you ever seen any big or interesting fish?
We will look forward to hearing from you.
Thanks for your questions. Here are some answers.
- We see different types
of animals on the seafloor. When we are exploring areas
away from the mid-ocean ridge we see brittle starfish, crinoids,
sea urchins, rat tail fish, and sea cucumbers (holothurians).
One of the students on board, Ben Wigham is a specialist
in holothurians and I’ll append some information
on these slimy creatures at the end of this message.
- We don’t see “active” volcanoes on the seafloor,
but we know they are there! Only a handful of submarine eruptions
on the mid-ocean ridge have been documented and studied in detail.
The first one was studied with Alvin in 1991 on the East Pacific
Rise near 9° 50’N. The other ones have mostly been
on the Juan de Fuca Ridge, part of the mid-ocean ridge system
off Washington State. Those were detected with the US Navy SOSUS
array (look in the “Hot Topics” section of
the website for more information on underwater acoustics
and detecting earthquakes and eruptions).
- Once, when diving in a
submersible off Hawaii I saw a 20 foot long shark at about
800 meters depth. It was VERY impressive. I think it was
attracted by the sub’s lights, I’m
glad it didn’t think we were lunch!
Thanks for your questions
and keep Diving and Discovering with us.
Holothurians - the “Sea-Cucumbers”
By Ben Wigham:
Holothurians are members
of a group of invertebrate animals called the Echinoderms,
which includes the starfish, sea urchins, and brittle stars.
Unlike their close relatives, holothurians have no arms or
spines, and their bodies are flattened. The animal is “stretched”, increasing the distance between its
mouth, giving it its characteristic “cucumber-like” shape.
All holothurians have a circle of tentacles surrounding their
mouth, which they can use to collect food. Shallow-water species
often stretch out their tentacles to collect plankton or other
food particles form the water column. Other holothurians, especially
those found in the deep sea, use their tentacles to sweep-up
the sediment or delicately pick at food particles on the seafloor.
Holothurians move about by using tube feet located on their underside.
They have a specialized “plumbing” system which allows
them to move water in and out of their tube feet to make them
move. Their tube feet also have suckers on the end to help them
Holothurians are very common animals in the deep sea. They are
one of the few groups of animal which can be found in the deepest
parts of the oceans where their soft bodies help them to cope
with the increased water pressure. There are currently over 400
recorded species of deep-sea holothurian, which can be found
in water deeper than 400m. Deep-sea species have many strange
body forms that are well adapted to their way of life. Some of
the animals collected in the North Atlantic Ocean have long tube
feet, to help them move over the soft muddy sediments, and some
hardly move at all, preferring to live in a burrow. Others don’t
really look like cucumbers at all; they may have big buoyant
tails or be flattened like a pancake. Some holothurians can even
When we look at photographs and video of the deep-sea floor,
such as those taken by Argo II, we don’t always see the
holothurians, but we often see the tracks they leave behind.
As the holothurian moves across the seafloor it leaves a trail
in the sediment. These tracks show up clearly on the video because,
when the holothurian moves, it disturbs the top-layer of the
sediment, often changing its color.
hi there, dive and discover!
First of all, you have a great site. but anyway, i have a question:
how do you carry enough oxygen? we are doing a project in school
where our team builds an underwater ocean lab. we would be staying
there for about a year. we are not allowed to go to the surface
to get anything, so how do you get oxygen? this is for homework,
so i would appreciate an answer ASAP!!!!!!
From Madeleine Webb, age 11, Atlanta GA
Thanks for your question. During expeditions 1 and 2 of Dive
and Discover, we used Alvin for our research. On this expedition
we don’t go, physically, to the bottom of the ocean; we
use the DSL-120 sonar and Argo mapping systems to show us the
When we dive in Alvin, it carries its own oxygen bottles and
the oxygen is slowly metered out into the personnel sphere. There
are also CO2 (carbon dioxide) scrubbers, which remove the CO2
that we breathe out by using different chemicals that bind up
the CO2 and take it out of the air. So for a SeaLab, you will
need both a supply of oxygen, either that is made using water
(a molecule which has 1 oxygen atom for each 2 hydrogen atoms),
or that is bottled. You'll also need some type of system that “scrubs” the
CO2 out of the air so that it does not accumulate as that can
give you headaches and hurt you if you breathe enough of it.
Hope this information helps you with your homework. Keep studying
hard, and Diving and Discovering with us.
Hi, are you running any longer summer expeditions lasting from
July - September as one of us is an Ocean Science student in
From Nikki White
Thanks for checking out the Dive and Discover website. After
this current expedition we are planning another one early next
year, in 2001, that will explore for hydrothermal vents in the
Indian Ocean near 24deg South Latitude. We will keep the website
up and running, and will be adding some additional information
modules, in the coming months.
Keep checking back and Diving and Discovering with us.
When Mt. St. Helens exploded, it literally blew the top of the
mountain many miles high and even more miles wide, turning former
rock to dust in the process. Assuming such events also occur
below the sea, do they ever explode with such force as to penetrate
through the sea to the surface and up into the atmosphere? If
so, it would be an awesome sight. On the other hand, given the
enormous weight of seawater, are such exploding forces insufficient
to penetrate through to the surface? What do you think?
Pete Minges, 4/10/00
Thanks for your question. You are correct that the pressure of
the water above the mid-ocean ridge axis, and the submarine
volcanoes there, keeps them from blowing their tops. Also,
the type of lava that is erupted is pretty fluid, like what
erupts in Hawaii- a basaltic lava, which usually does not erupt
explosively, like Mt. St. Helens. One main reason why basaltic
lavas erupt less explosively is that they have less silica
(SiO2) in them, usually about 48-53 weight percent, compared
to rocks (called dacites and rhyolites) from volcanoes that
explode which have more silica in them- often greater than
60 weight percent. The less silica in the magma cause it to
be more fluid because there are fewer silicon dioxide molecules
to make strong bonds with other atoms in the magma.
One other factor is that basalts don’t have much gas
in them, while rocks that erupt in explosive volcanoes have
Hope this answers your question. Thanks for Diving and Discovering